Cardiac pacing sensing and control

ABSTRACT

A cardiac pacing system having a pulse generator for generating therapeutic electric pulses, a lead electrically coupled with the pulse generator having an electrode, a first sensor configured to monitor a physiological characteristic of a patient, a second sensor configured to monitor a second physiological characteristic of a patient and a controller. The controller can determine a pacing vector based on variables including a signal received from the second sensor, and cause the pulse generator to deliver the therapeutic electrical pulses according to the determined pacing vector. The controller can also modify pacing characteristics based on variables including a signal received from the second sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to and thebenefit of U.S. Pat. No. 15,494,126 titled Cardiac Pacing Sensing AndControl, filed Apr. 21, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/951,277 titled Cardiac Pacing Sensing AndControl, filed Nov. 24, 2015, which claims priority to and benefit ofU.S. Provisional Patent Application No. 62/083,516 titled ImplantableMedical Device with Pacing Therapy, filed Nov. 24, 2014, U.S.Provisional Patent Application No. 62/146,569 titled Delivery Systemsand Implantable Leads for Intracostal Pacing, filed Apr. 13, 2015, andis a continuation-in-part of U.S. patent application Ser. No.14/846,710, filed Sep. 4, 2015 and titled Cardiac Pacing, U.S. patentapplication Ser. No. 14/846,686, filed Sep. 4, 2015 and titledReceptacle for a Pacemaker Lead, and U.S. patent application Ser. No.14/846,648, filed Sep. 4, 2015 and titled Delivery System for CardiacPacing, the disclosures of which are incorporated herein by reference intheir entirety.

TECHNICAL FIELD

The subject matter described herein relates to devices, systems andmethods for cardiac pacing.

BACKGROUND

An artificial pacemaker is a medical device that helps control abnormalheart rhythms. A pacemaker uses electrical pulses to prompt the heart tobeat at a normal rate. The pacemaker may speed up a slow heart rhythm,control a fast heart rhythm, and coordinate the chambers of the heart.The implantable portions of a pacemaker system generally comprise threemain components: a pulse generator, one or more wires called leads, andelectrodes found on each lead. The pulse generator produces theelectrical signals that make the heart beat. Most pulse generators alsohave the capability to receive and respond to signals that are sent bythe heart. Leads are insulated flexible wires that conduct electricalsignals to the heart from the pulse generator. The leads may also relaysignals from the heart to the pulse generator. One end of the lead isattached to the pulse generator and the electrode end of the lead ispositioned on or in the heart.

SUMMARY

In one aspect, a cardiac pacing system is described. The cardiac pacingsystem can include a pulse generator. The pulse generator can include ahousing. The pulse generator can be configured to generate therapeuticelectric pulses. The cardiac pacing system can include at least onelead. The at least one lead can be configured to electrically couplewith the pulse generator. The at least one lead can include anelectrode. The cardiac pacing system can include a first sensor. Thefirst sensor can be configured to monitor a physiological characteristicof a patient. The cardiac pacing system can include a second sensor. Thesecond sensor can be configured to monitor a second physiologicalcharacteristic of a patient.

The cardiac pacing system can include a controller. The controller canbe configured to determine a pacing vector. The pacing vector can bebased on variables. The variables can include a signal received from thesecond sensor. The controller can be configured to cause the pulsegenerator to deliver the therapeutic electrical pulses according to thedetermined pacing vector.

In some variations, the first sensor can be an electrode configured tosense heart rate. The controller can be configured to determine a pacingvector based on variables including a signal received from the firstsensor.

The housing of the pulse generator can include at least one housingelectrode. The at least one housing electrode can be configured to actas a sensor or as an electrode. The controller can be configured todetermine a pacing vector based on at least a signal transmitted fromthe housing electrode.

In some variations, the controller can be configured to cause the pulsegenerator to deliver the therapeutic electrical pulses from more thanone electrode. The therapeutic electrical pulses can be delivered in amanner where more than one electrode acts as a cathode and more than oneelectrode acts as an anode.

In some variations, the second sensor can be an accelerometer, anacoustic sensor, or the like. The variables can include a sensed amountof skeletal muscle stimulation during pacing, a sensed posture of thepatient, a sensed heart rate of the patient, the energy required bypotential pacing vectors, the distance between an electrode utilized fordelivery of the therapeutic electrical pulses and a sensor, or the like.

In some variations, the controller can be configured to utilize aweighted scoring method in determining the pacing vector. The controllercan be configured for a vector selection assessment. A patientperception of discomfort can be considered in the vector selectionassessment. The controller can be configured to determine the pacingvector based on results of the vector selection assessment.

In another aspect, a cardiac pacing system is described. The cardiacpacing system can include a pulse generator configured to generatetherapeutic electric pulses. The cardiac pacing system can include atleast one lead configured to electrically couple with the pulsegenerator, the at least one lead including an electrode. The cardiacpacing system can include a first sensor configured to monitor acharacteristic of a patient. The cardiac pacing system can include asecond sensor configured to monitor a second characteristic of apatient. The cardiac pacing system can include a controller. Thecontroller can be configured to modify pacing characteristics based onvariables including a signal received from the second sensor. Thecontroller can be configured to cause the pulse generator to deliver thetherapeutic electrical pulses according to the determined modifiedpacing characteristics.

In some variations, the pacing characteristics can be selected from thegroup consisting of pacing vector, pulse energy and pulse width.

The first sensor can be an electrode. The electrode can be configured tosense heart rate. The controller can be configured to modify pacingcharacteristics based on variables including a signal received from thefirst sensor. The second sensor can be a multi-axis accelerometerconfigured to monitor a posture of the patient. The controller can beconfigured to modify pacing characteristics in a manner proportional toa change in posture.

In some variations, the controller can be further configured to operatewith a programmer to develop empirical data to assist in modifyingpacing characteristics based on posture. The empirical data comprisespacing characteristics required for different postures.

The second sensor can be an accelerometer configured to monitor skeletalmuscle deflection. The controller can be configured to modify pacingcharacteristics includes comparing the signal from the accelerometerduring pacing to the signal from the accelerometer during intrinsicheartbeat activity. The controller can be configured to operate with aprogrammer to develop empirical data to assist in modifying pacingcharacteristics based on skeletal muscle deflection. The empirical datacan include pacing characteristics correlated with patient discomfort.

The second sensor can be configured to determine R-wave intervals. Thecontroller can be configured to determine an interval threshold based onsensed R-wave intervals. The controller can be configured to modifypacing characteristics by providing for a pacing pulse when the intervalthreshold is reached without detection of an intrinsic R-wave.

The controller can be configured to modify pacing characteristics bylimiting the pacing characteristics to a ventricular pacing rate notexceeding a maximum ventricular tracking rate threshold. The controllercan be configured to modify pacing characteristics by switching to anon-tracking mode in response to the sensing of a prolonged, highlyvariable or high rate atrial arrhythmia.

In another aspect, a computer-readable medium storing instructions isdescribed. The instructions, when implemented by a programmableprocessor, can cause one or more operations to be performed. The one ormore operations can include one or more of the operations described inrelation to the cardiac pacing systems described herein. Theprogrammable processor can be a programmable processor included in thecardiac pacing system.

The details of one or more variations of the subject matter describedherein are set forth in the accompanying drawings and the descriptionbelow. Other features and advantages of the subject matter describedherein will be apparent from the description and drawings, and from theclaims. While certain features of the currently disclosed subject matterare described for illustrative purposes, it should be readily understoodthat such features are not intended to be limiting. The claims thatfollow this disclosure are intended to define the scope of the protectedsubject matter.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, show certain aspects of the subject matterdisclosed herein and, together with the description, help explain someof the principles associated with the disclosed implementations. In thedrawings,

FIG. 1 is a front-view of an exemplary pulse generator having featuresconsistent with implementations of the current subject matter;

FIG. 2 is a rear-view of an exemplary pulse generator having featuresconsistent with implementations of the current subject matter;

FIG. 3 is an illustration of a simplified schematic diagram of anexemplary pulse generator having features consistent withimplementations of the current subject matter;

FIG. 4A is an illustration showing exemplary placements of elements of acardiac pacing system having features consistent with the currentsubject matter;

FIG. 4B is an illustration showing exemplary placements of elements of acardiac pacing system having features consistent with the currentsubject matter;

FIG. 4C is a cross-sectional illustration of a thoracic region of apatient;

FIG. 5 is an illustration of an exemplary method of implanting a cardiacpacing system into a patient having features consistent with the currentsubject matter;

FIG. 6A is an illustration of an exemplary delivery system for a pulsegenerator having features consistent with implementations of the currentsubject matter;

FIG. 6B is an illustration of an exemplary delivery system with a pulsegenerator disposed therein consistent with implementations of thecurrent subject matter;

FIG. 7 is an illustration of an exemplary process flow illustrating amethod of placing a pacing lead having features consistent with thecurrent subject matter;

FIG. 8A is an illustration of an exemplary lead having featuresconsistent with the current subject matter;

FIG. 8B is an illustration of an exemplary lead having featuresconsistent with the current subject matter;

FIG. 9A is an illustration of the distal end of an exemplary deliverysystem having features consistent with the current subject matter;

FIG. 9B is an illustration of an exemplary process for using thedelivery system illustrated in FIG. 9A;

FIG. 10 is a schematic illustration of an exemplary delivery controlsystem having features consistent with the current subject matter;

FIGS. 11A and 11B are illustrations of an exemplary lead having featuresconsistent with the current subject matter;

FIG. 12 is an illustration of an exemplary sheath for delivering a lead,the sheath having features consistent with the current subject matter;

FIG. 13 is an illustration of an intercostal space associated with thecardiac notch of the left lung with an exemplary lead fixationreceptacle having features consistent with the current subject matterinserted therein;

FIG. 14 is an illustration of an exemplary lead fixation receptaclehaving features consistent with the current subject matter;

FIG. 15 is an illustration of an exemplary lead fixation receptaclehaving features consistent with the current subject matter; and,

FIG. 16 is an illustration of an exemplary lead fixation receptaclehaving features consistent with the current subject matter.

FIGS. 17A and 17B are illustrations of an exemplary data flow forsensing signals and signal preparation for cardiac therapy havingfeatures consistent with the present disclosure;

FIG. 18 is an illustration of an exemplary process flow for alteringsoftware filters and the active baseline algorithm, having featuresconsistent with the present disclosure;

FIG. 19A is a graph of an example of an ECG of a heart;

FIG. 19B is a graph of a simultaneous acoustic signal as the ECG signalshown in FIG. 19A;

FIG. 20 is an illustration of an exemplary process flow for processingacoustic signals obtained by the cardiac pacing system, having featuresconsistent with the present disclosure;

FIG. 21A is an illustration of an exemplary process flow for an atrialtemplate reference having features consistent with the presentdescription;

FIG. 21B is an illustration of a P-wave signal indicating the“expectation window”;

FIG. 22 is an illustration of an exemplary process flow for analyzingsensed signals for the triggering and authentication of heartbeatdetections, having features consistent with the present disclosure;

FIG. 23 is an illustration of an ECG reading over time together with atime synchronized heart sound signal reading over time having featuresconsistent with the present disclosure;

FIG. 24 is an exemplary process flow for verifying a lack of heart beathaving features consistent with the current subject matter; and,

FIG. 25 is an illustration of an exemplary process flow for analyzingsensed signals to determine whether delivered energy levels and/orpacing vectors can be adjusted, having features consistent with thepresent disclosure.

When practical, similar reference numbers denote similar structures,features, or elements.

DETAILED DESCRIPTION

Implantable medical devices (IMDs), such as cardiac pacemakers orimplantable cardioverter defibrillators (ICDs), provide therapeuticelectrical stimulation to the heart of a patient. This electricalstimulation may be delivered via electrodes on one or more implantableendocardial or epicardial leads that are positioned in or on the heart.This electrical stimulation may also be delivered using a leadlesscardiac pacemaker disposed within a chamber of the heart. Therapeuticelectrical stimulation may be delivered to the heart in the form ofelectrical pulses or shocks for pacing, cardioversion or defibrillation.

An implantable cardiac pacemaker may be configured to facilitate thetreatment of cardiac arrhythmias. The devices, systems and methods ofthe present disclosure may be used to treat cardiac arrhythmiasincluding, but not limited to, bradycardia, tachycardia, atrial flutterand atrial fibrillation. Resynchronization pacing therapy may also beprovided.

A cardiac pacemaker consistent with the present disclosure may include apulse generator implanted adjacent the rib cage of the patient, forexample, on the ribcage under the pectoral muscles, laterally on theribcage, within the mediastinum, subcutaneously on the sternum of theribcage, and the like. One or more leads may be connected to the pulsegenerator. A lead may be inserted, for example, between two ribs of apatient so that the distal end of the lead is positioned within themediastinum of the patient adjacent, but not touching, the heart. Thedistal end of the lead may include an electrode for providing electricalpulse therapy to the patient's heart and may also include at least onesensor for detecting a state of the patient's organs and/or systems. Thecardiac pacemaker may include a unitary design where the components ofthe pulse generator and lead are incorporated within a single formfactor. For example, where a first portion of the unitary device resideswithin the subcutaneous tissue and a second portion of the unitarydevice is placed through an intercostal space into a location within themediastinum.

FIG. 1 is a front-view 100 of a pulse generator 102 having featuresconsistent with implementations of the current subject matter. The pulsegenerator 102 may be referred to as a cardiac pacemaker. The pulsegenerator 102 can include a housing 104, which may be hermeticallysealed. In the present disclosure, and commonly in the art, housing 104and everything within it may be referred to as a pulse generator,despite there being elements inside the housing other than those thatgenerate pulses (for example, processors, storage, battery, etc.).

Housing 104 can be substantially rectangular in shape and the first endof the housing 104 may include a tapered portion 108. The taperedportion can include a first tapered edge 110, tapered inwardly towardthe transverse plane. The tapered portion 108 can include a secondtapered edge 112 tapered inwardly toward the longitudinal plane. Each ofthe first tapered edge 110 and the second tapered edge 112 may have asimilar tapered edge generally symmetrically disposed on the oppositeside of tapered portion 108, to form two pairs of tapered edges. Thepairs of tapered edges may thereby form a chisel-shape at the first end106 of pulse generator 102. When used in the present disclosure, theterm “chisel-shape” refers to any configuration of a portion of housing104 that facilitates the separation of tissue planes during placement ofpulse generator 102 into a patient. The “chisel-shape” can facilitatecreation of a tightly fitting and properly sized pocket in the patient'stissue in which the pulse generator may be secured. For example, achisel-shape portion of housing 104 may have a single tapered edge, apair of tapered edges, 2 pairs of tapered edges, and the like.Generally, the tapering of the edges forms the shape of a chisel or theshape of the head of a flat head screwdriver. In some variations, thesecond end 114 of the pulse generator can be tapered. In othervariations, one or more additional sides of the pulse generator 102 canbe tapered.

Housing 104 of pulse generator 102 can include a second end 114. Thesecond end 114 can include a port assembly 116. Port assembly 116 can beintegrated with housing 104 to form a hermetically sealed structure.Port assembly 116 may be configured to facilitate the egress ofconductors from housing 104 of pulse generator 102 while maintaining aseal. For example, port assembly 116 may be configured to facilitate theegress of a first conductor 118 and a second conductor 120 from housing104. The first conductor 118 and the second conductor 120 may combinewithin port assembly 116 to form a twin-lead cable 122. In somevariations, the twin-lead cable 122 can be a coaxial cable. Thetwin-lead cable 122 may include a connection port 124 remote fromhousing 104. Connection port 124 can be configured to receive at leastone lead, for example, a pacing lead. Connection port 124 of the cable122 can include a sealed housing 126. Sealed housing 126 can beconfigured to envelope a portion of the received lead(s) and form asealed connection with the received lead(s).

Port assembly 116 may be made from a different material than housing104. For example, housing 104 may be made from a metal alloy and portassembly 116 may be made from a more flexible polymer. While portassembly 116 may be manufactured separately from housing 104 and thenintegrated with it, port assembly 116 may also be designed to be part ofhousing 104 itself. The port assembly 116 may be externalized from thehousing 104 as depicted in FIG. 1. The port assembly 116 may beincorporated within the shape of housing 104 of pulse generator 102.

FIG. 2 is a rear-view 200 of pulse generator 102 showing the back-side128 of housing 104. As shown, pulse generator 102 can include one ormore electrodes or sensors disposed within housing 104. As depicted inthe example of FIG. 2, housing 104 includes a first in-housing electrode130 and a second in-housing electrode 132. The various electrodesillustrated and discussed herein may be used for delivering therapy tothe patient, sensing a condition of the patient, and/or a combinationthereof. A pulse generator consistent with the present disclosureinstalled at or near the sternum of a patient can monitor the heart,lungs, major blood vessels, and the like through sensor(s) integratedinto housing 104.

FIG. 3 is an illustration 300 of a simplified schematic diagram of anexemplary pulse generator 102 having features consistent with thecurrent subject matter. Pulse generator 102 can include signalprocessing and therapy circuitry to detect various cardiac conditions.Cardiac conditions can include ventricular dyssynchrony, arrhythmiassuch as bradycardia and tachycardia conditions, and the like. Pulsegenerator 102 can be configured to sense and discriminate atrial andventricular activity and then deliver appropriate electrical stimuli tothe heart based on a sensed state of the heart.

Pulse generator 102 can include one or more components. The one or morecomponents may be hermetically sealed within the housing 104 of pulsegenerator 102. Pulse generator 102 can include a controller 302,configured to control the operation of the pulse generator 102. Thepulse generator 102 can include an atrial pulse generator 304 and mayalso include a ventricular pulse generator 306. Controller 302 can beconfigured to cause the atrial pulse generator 304 and the ventricularpulse generator 306 to generate electrical pulses in accordance with oneor more protocols that may be loaded onto controller 302. Controller 302can be configured to control pulse generators 304, 306, to deliverelectrical pulses with the amplitudes, pulse widths, frequency, orelectrode polarities specified by the therapy protocols, to one or moreatria or ventricles.

Controller electronic storage 308 can store instructions configured tobe implemented by the controller to control the functions of pulsegenerator 102.

Controller 302 can include a processor(s). The processor(s) can includeany one or more of a microprocessor, a controller, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or equivalent discrete or analoglogic circuitry. The functions attributed to controller 302 herein maybe embodied as software, firmware, hardware or any combination thereof.

The pulse generator 102 can include a battery 310 to power thecomponents of the pulse generator 102. In some variations, battery 310can be configured to charge a capacitor. Atrial pulse generator 304 andventricular pulse generator 306 can include a capacitor charged by thebattery 310. The electrical energy stored in the capacitor(s) can bedischarged as controlled by controller 302. The electrical energy can betransmitted to its destination through one or more electrode leads 312,314. The leads can include a ventricular pulsing lead 312, an atrialpulsing lead 314, and/or other leads.

Pulse generator 102 can include one or more sensors 322. Sensor(s) 322can be configured to monitor various aspects of a patient's physiology.Sensor(s) 322 may be embedded in the housing of pulse generator 102,incorporated into leads 312, 314 or be incorporated into separate leads.Sensors 322 of pulse generator 102 can be configured to detect, forexample, signals from a patient's heart. The signals can be decoded bycontroller 302 of the pulse generator to determine a state of thepatient. In response to detecting a cardiac arrhythmia, controller 302can be configured to cause appropriate electrical stimulation to betransmitted through electrodes 312 and 314 by atrial pulse generator 304and/or ventricular pulse generator 306.

Sensor(s) 322 can be further configured to detect other physiologicalstates of the patient, for example, a respiration rate, blood oximetry,and/or other physiological states. In variations where the pulsegenerator 102 utilizes a plurality of electrodes, controller 302 may beconfigured to alter the sensing and delivery vectors between availableelectrodes to enhance the sensitivity and specificity of arrhythmiadetection and improve efficacy of the therapy delivered by theelectrical impulses from the pulse generator 102.

Pulse generator 102 can include a transceiver 316. The transceiver caninclude an antenna 318. The transceiver 316 can be configured totransmit and/or receive radio frequency signals. The transceiver 316 canbe configured to transmit and/or receive wireless signals having anywireless communication protocol. Wireless communication protocols caninclude Bluetooth, Bluetooth low energy, Near-Field Communication, WiFi,and/or other radio frequency protocols. The transceiver 316 can beconfigured to transmit and/or receive radio frequency signals to and/orfrom a programmer 320. The programmer 320 can be a computing deviceexternal to the patient. Programmer 320 may comprise a transceiverconfigured to transmit and/or receive radio frequency signals to and/orfrom the transceiver 316 of the pulse generator 102. Transceiver 316 canbe configured to wirelessly communicate with programmer 320 throughinduction, radio-frequency communication or other short-rangecommunication methodologies.

In some variations, programmer 320 can be configured to communicate withthe pulse generator 102 through longer-range remote connectivitysystems. Such longer-range remote connectivity systems can facilitateremote access, by an operator, to pulse generator 102 without theoperator being in close proximity with the patient. Longer-range remoteconnectivity systems can include, for example, remote connectivitythrough the Internet, and the like. When an operator connects with pulsegenerator 102 through longer-range remote connectivity systems, a localdevice can be positioned within a threshold distance of the patient. Thelocal device can communicate using one or more radio-frequency wirelessconnections with the pulse generator 102. The local device can, in turn,include hardware and/or software features configured to facilitatecommunication between it and an operator device at which the operator isstationed. The local device can be, for example, a mobile computingdevice such as a smartphone, tablet, laptop, and the like. The localdevice can be a purpose-built local device configured to communicatewith the pulse generator 102. The local device can be paired with thepulse generator 102 such that the communications between the pulsegenerator 102 and the local device are encrypted. Communications betweenthe local device and the operator device can be encrypted.

Programmer 320 can be configured to program one or more parameters ofthe pulse generator 102. The parameter(s) can include timing of thestimulation pulses of the atrial pulse generator, timing of thestimulation pulses of the ventricular pulse generator, timing of pulsesrelative to certain sensed activity of the anatomy of the patient, theenergy levels of the stimulation pulses, the duration of the stimulationpulses, the pattern of the stimulation pulses and other parameters. Theprogrammer 320 can facilitate the performance of diagnostics on thepatient or the pulse generator 102.

Programmer 320 can be configured to facilitate an operator of theprogrammer 320 to define how the pulse generator 102 senses electricalsignals, for example ECGs, and the like. The programmer 320 canfacilitate an operator of the programmer 320 to define how the pulsegenerator 102 detects cardiac conditions, for example ventriculardyssynchrony, arrhythmias, and the like. The programmer 320 canfacilitate defining how the pulse generator 102 delivers therapy, andcommunicates with other devices.

An operator can fine-tune parameters through the programmer 320. Forexample, the sensitivity of sensors embodied in the housing of the pulsegenerator 302, or within leads, can be modified. Programmer 320 canfacilitate setting up communication protocols between the pulsegenerator 102 and another device such as a mobile computing device.Programmer 320 can be configured to facilitate modification of thecommunication protocols of the pulse generator 102, such as addingsecurity layers, or preventing two-way communication. Programmer 320 canbe configured to facilitate determination of which combination ofimplanted electrodes are best suited for sensing and therapy delivery.

Programmer 320 can be used during the implant procedure. For example,programmer 320 can be used to determine if an implanted lead ispositioned such that acceptable performance will be possible. If theperformance of the system is deemed unacceptable by programmer 320, thelead may be repositioned by the physician, or an automated deliverysystem, until the lead resides in a suitable position. Programmer 320can also be used to communicate feedback from sensors disposed on theleads and housing 104 during the implant procedure.

In some cases, concomitant devices such as another pacemaker, an ICD, ora cutaneous or implantable cardiac monitor, can be present in a patient,along with pulse generator 102. Pulse generator 102 can be configured tocommunicate with such concomitant devices through transceiver 316wirelessly, or the concomitant device may be physically connected topulse generator 102. Physical connection between devices may beaccomplished using a lead emanating from pulse generator 102 that iscompatible with the concomitant device. For example, the distal end of alead emanating from pulse generator 102 may be physically andelectrically connected to a port contained on the concomitant device.Physical connection between devices may also be accomplished using animplantable adaptor that facilitates electrical connection between thelead emanating from pulse generator 102 and the concomitant device. Forexample, an adapter may be used that will physically and electricallycouple the devices despite not having native components to facilitatesuch connection. Concomitant devices may be connected using a “smartadapter” that provides electrical connection between concomitant devicesand contains signal processing capabilities to convert signal attributesfrom each respective device such that the concomitant devices arefunctionally compatible with each other.

Pulse generator 102 can be configured to have a two-way conversation ora one-way conversation with a concomitant device. Controller 302 can beconfigured to cause the concomitant device to act in concert with pulsegenerator 102 when providing therapy to the patient, or controller 302can gather information about the patient from the concomitant device. Insome variations, pulse generator 102 can be configured to be triggeredvia one-way communication from a concomitant device to pulse generator102.

FIGS. 4A and 4B are illustrations showing exemplary placements ofelements of a cardiac pacing system having features consistent with thepresent disclosure. Pulse generator 102 can be disposed in a patient,adjacent an outer surface of ribcage 404. For example, pulse generator102 can be disposed on the sternum 402 of the patient's ribcage 404. Alead 414, attached to pulse generator 102, may also be disposed in thepatient by traversing through intercostal muscle 410 of the patient.Lead 414 may optionally pass through a receptacle 408 in intercostalmuscle 410 to guide the lead, fix the lead, and/or electrically insulatethe lead from the tissue of the intercostal muscle 410 (examples of suchreceptacles are described herein with respect to FIGS. 13-16).

In other variations, pulse generator 102 can be disposed outside of apatient's ribcage in a pectoral position, outside of the patient'sribcage in a lateral position, below (inferior to) the patient's ribcagein a subxiphoid or abdominal position, within the patient's mediastinum,or the like.

Lead 414 may be passed through the ribcage so the distal end of the leadand its electrodes are disposed on, or pass through, the inner surfaceof the rib or inner surface of the innermost intercostal muscle, or mayalternatively traverse further within the thoracic cavity, but withoutphysically contacting the tissue comprising the heart. This placementmay be referred to herein as intracostal or intracostally.

Leads may be inserted between any two ribs within the thoracic cavity,for example, as shown in FIG. 4A. In some variations, it is desirable toinsert the lead through one of the intercostal spaces associated withcardiac notch of the left lung 420. For example, between the fourth andfifth ribs or between the fifth and sixth ribs. Due to variations inanatomy, the rib spacing associated with the cardiac notch of the leftlung 420 may differ. In some patients the cardiac notch of the left lung420 may not be present or other cardiac anomalies such as dextrocardiamay require the insertion through alternative rib spaces. Lead 414 maybe inserted into such a location through an incision 406, as shown inFIG. 4A. Lead 414 may optionally be inserted into such a locationthrough a receptacle 408, as shown in FIG. 4B.

Precise placement of a distal end of lead 414, which may includeelectrode(s) for pacing or sensing, is now described further withreference to the anatomical illustrations of FIGS. 4A, 4B and 4C. Insome variations, the distal end of lead 414 can be located within theintercostal space or intercostal muscle 410. In such variations, thedistal end of lead 414 is preferably surrounded by a receptacle 408 thatelectrically insulates the distal end of the lead 414 from theintercostal muscle 410. In another variation, the distal end of lead 414may be placed just on the inner surface of a rib or on the inner surfaceof the innermost intercostal muscle.

The distal end of lead 414 can also be positioned so as to abut theparietal pleura of the lung 426. In other variations, the distal end oflead 414 can be positioned so as to terminate within the mediastinum 428of the thoracic cavity of the patient, proximate the heart 418, but notphysically in contact with the heart 418 or the pericardium 432 of heart418. Alternatively, the distal end of lead 414 can be placed to abut thepericardium 432, but not physically attach to the epicardial tissuecomprising the heart.

The distal end of lead 414 may be physically affixed to cartilage orbone found within the thoracic cavity, for example, to a rib, tocartilage of a rib, or to other bone or cartilage structure in thethoracic cavity. In one variation, the lead can be disposed such that itis wrapped around the patient's sternum 402.

For certain placements, lead 414 can be adequately fixed by directphysical contact with surrounding tissue. In other variations, anadditional fixation mechanism may be used. For example, the distal endof lead 414 can incorporate a fixation mechanism such as a tine, hook,spring, screw, or other fixation device. The fixation mechanism can beconfigured to secure the lead in the surrounding tissue, cartilage,bone, or other tissue, to prevent the lead from migrating from itsoriginal implantation location.

FIG. 5 is an illustration 500 of an exemplary method of implanting acardiac pacing system into a patient consistent with the presentdisclosure. At 502, a pulse generator 102 may be implanted, in a mannerdescribed above, adjacent the sternum 402 of a patient. Optionally,pulse generator 102 may be at least partially chisel-shaped tofacilitate implantation and the separation of tissue planes. At 504, alead 414 may be inserted into an intercostal space 410 of a patient. Asdescribed above, lead 414 may optionally be inserted into a receptacle408 disposed within intercostal space 410. At 506, the distal end oflead 414 is delivered to one of a number of suitable final locations forpacing, as described above.

FIG. 6A is an illustration 600 of a pulse generator delivery system 602for facilitating positioning of pulse generator 102 into a patient, thedelivery system 602 having features consistent with the current subjectmatter. FIG. 6B is an illustration 604 of the delivery system 602 asillustrated in FIG. 6A with the pulse generator 102 mounted in it.Delivery system 602 can be configured to facilitate implantation of thepulse generator 102 into the thoracic region of a patient.

Delivery system 602 includes a proximal end 606 and a distal end 608.The distal end 608 of delivery system 602 contains a receptacle 610 inwhich the housing of the pulse generator 102 is loaded. Where the pulsegenerator 102 contains a connection lead, the delivery system 602 can beconfigured to accommodate the connection lead so that the connectionlead will not be damaged during the implantation of the pulse generator102.

When pulse generator 102 is fully loaded into delivery system 602, pulsegenerator 102 is substantially embedded into the receptacle 610. In somevariations, a portion of the pulse generator 102's distal end can beexposed, protruding from the end of receptacle 610. The tapered shape ofthe distal end 106 of pulse generator 102 can be used in conjunctionwith the delivery system 602 to assist with separating tissue planes asdelivery system 602 is used to advance pulse generator 102 to itsdesired location within the patient.

In some variations, the entirety of pulse generator 102 can be containedwithin receptacle 610 of the delivery system 602. The pulse generator102 in such a configuration will not be exposed during the initialadvancement of delivery system 602 into the patient. The distal end 608of delivery system 602 may be designed to itself separate tissue planeswithin the patient as delivery system 602 is advanced to the desiredlocation within the patient.

The pulse generator delivery system 602 may be made from a polymer, ametal, a composite material or other suitable material. Pulse generatordelivery system 602 can include multiple components. Each component ofthe pulse generator delivery system 602 can be formed from a materialsuitable to the function of the component. The pulse generator deliverysystem 602 can be made from a material capable of being sterilized forrepeated use with different patients.

Pulse generator delivery system 602 may include a handle 612. Handle 612can facilitate advancement of delivery system 602 and pulse generator102 into a patient's body. Handle 612 can be disposed on either side ofthe main body 614 of the delivery system 602, as illustrated in FIGS. 6Aand 6B. In some variations, handle 612 can be disposed on just one sideof the main body 614 of the delivery system 602. The handle 612 can beconfigured to be disposed parallel to plane of insertion and advancement616 of pulse generator delivery system 602 within the body. In somevariations, handle 612 can be located orthogonally to the plane ofinsertion and advancement 616 of the delivery system 602. Handle 612 canbe configured to facilitate the exertion of pressure, by a physician,onto the pulse generator delivery system 602, to facilitate theadvancement and positioning of the delivery system 602 at the desiredlocation within the patient.

Pulse generator delivery system 602 can include a pulse generatorrelease device 618. The release device 618 can be configured tofacilitate disengagement of the pulse generator 102 from the deliverysystem 602. In some variations, release device 618 can include a plunger620. Plunger 620 can include a distal end configured to engage with theproximal end 606 of the pulse generator delivery system 602. The plunger620 can engage with the proximal end 606 of the pulse generator deliverysystem 602 when the pulse generator 102 is loaded into the receptacle610 of the delivery system 602. The proximal end 622 of the plunger 620can extend from the proximal end 606 of the delivery system 602.

Plunger 620 can include a force applicator 624. Force applicator 624 canbe positioned at the proximal end 622 of plunger 620. Force applicator624 can be configured to facilitate application of a force to theplunger 620 to advance the plunger 620. Advancing plunger 620 can forcepulse generator 102 from the delivery system 602. In some variations,the force applicator 624 can be a ring member. The ring member canfacilitate insertion, by the physician, of a finger. Pressure can beapplied to the plunger 620 through the ring member, forcing the pulsegenerator 102 out of the receptacle 610 of the delivery system 602 intothe patient at its desired location. In some variations, the proximalend 622 of the plunger 620 can include a flat area, for example, similarto the flat area of a syringe, that allows the physician to applypressure to the plunger 620. In some variations, the plunger 620 can beactivated by a mechanical means such as a ratcheting mechanism.

The distal end 608 of the pulse generator delivery device 602 caninclude one or more sensors. The sensor(s) can be configured tofacilitate detection of a state of patient tissues adjacent distal end608 of the pulse generator delivery device 602. Various patient tissuescan emit, conduct and/or reflect signals. The emitted, conducted and/orreflected signals can provide an indication of the type of tissueencountered by the distal end 608 of the pulse generator delivery device602. Such sensor(s) can be configured, for example, to detect theelectrical impedance of the tissue adjacent the distal end 608 of thepulse generator delivery device 602. Different tissues can havedifferent levels of electrical impedance. Monitoring the electricalimpedance can facilitate a determination of the location, or tissueplane, of the distal end 608 of the delivery device 602.

In addition to delivery of the pulse generator, delivery of at least onelead for sensing and/or transmitting therapeutic electrical pulses fromthe pulse generator is typically required. Proper positioning of thedistal end of such lead(s) relative to the heart is very important.Delivery systems are provided that can facilitate the insertion of oneor more leads to the correct location(s) in the patient. The deliverysystems can facilitate finding the location of the initial insertionpoint for the lead. The initial insertion point optionally being anintercostal space associated with a patient's cardiac notch of the leftlung. The intercostal spaces associated with the cardiac notch commonlyinclude the left-hand-side fourth, fifth and sixth intercostal spaces.Other intercostal spaces on either side of the sternum may be used,especially when the patient is experiencing conditions that prevent useof the fourth, fifth and sixth intercostal spaces, or due to anatomicalvariations.

When making the initial insertion through the epidermis and theintercostal muscles of the patient, it is important to avoid damagingimportant blood-filled structures of the patient. Various techniques canbe employed to avoid damaging important blood-filled structures. Forexample, sensors can be used to determine the location of theblood-filled structures. Such sensors may include accelerometersconfigured to monitor pressure waves caused by blood flowing through theblood-filed structures. Sensors configured to emit and detectlight-waves may be used to facilitate locating tissues that absorbcertain wavelengths of light and thereby locate different types oftissue. Temperature sensors may be configured to detect differences intemperature between blood-filled structures and surrounding tissue.Lasers and detectors may be employed to scan laser light across thesurface of a patient to determine the location of subcutaneousblood-filled structures.

Conventional medical devices may be employed to locate the desiredinitial insertion point into the patient. For example, x-ray machines,MRI machines, CT scanning machines, fluoroscopes, ultrasound machinesand the like, may be used to facilitate determination of the initialinsertion point for the leads as well as facilitate in advancing thelead into the patient.

Advancing a lead into a patient can also present the risk of damagingphysiological structures of the patient. Sensors may be employed tomonitor the characteristics of tissues within the vicinity of the distalend of an advancing lead. Readings from sensors associated with thecharacteristics of tissues can be compared against known characteristicsto determine the type of tissue in the vicinity of the distal end of theadvancing lead.

Sensors, such as pH sensors, thermocouples, accelerometers, electricalimpedance monitors, and the like, may be used to detect the depth of thedistal end of the electrode in the patient. Physiologicalcharacteristics of the body change the further a lead ventures into it.Measurements performed by sensors at, or near, the distal end of theadvancing lead may facilitate the determination of the type of tissue inthe vicinity of the distal end of the lead, as well as its depth intothe patient.

Various medical imaging procedures, may be used on a patient todetermine the location of the desired positions in the heart for thedistal end of the lead(s). This information can be used, in conjunctionwith sensor readings, of the kind described herein, to determine whenthe distal end of the lead has advanced to a desired location within thepatient.

Components may be used to first create a channel to the desired locationfor the distal end of the lead. Components can include sheathes,needles, cannulas, balloon catheters and the like. A component may beadvanced into the patient with the assistance of sensor measurements todetermine the location of the distal end of the component. Once thecomponent has reached the desired location, the component may bereplaced with the lead or the lead may be inserted within the component.An example of a component can include an expandable sheath. Once thesheath has been advanced to the desired location, a cannula extendingthe length of the sheath may be expanded, allowing a lead to be passthrough the cannula. The sheath may then be removed from around thelead, leaving the lead in situ with the distal end of the lead at thedesired location.

Determination of the final placement of the distal end of a lead isimportant for the delivery of effective therapeutic electrical pulsesfor pacing the heart. The present disclosure describes multipletechnologies to assist in placement of a lead in the desired location.For example, the use of sensors on the pulse generator, on the distalend of leads, or on delivery components. In addition, when a lead orcomponent is advanced into a patient, balloons may be employed to avoiddamaging physiological structures of the patient. Inflatable balloonsmay be disposed on the distal end of the lead or component, on the sidesof a lead body of the lead, or may be circumferentially disposed aboutthe lead body. The balloons may be inflated to facilitate thedisplacement of tissue from the lead to avoid causing damage to thetissue by the advancing lead. A lead delivery assembly may also be usedto facilitate delivery of the lead to the desired location. In somevariations, the lead delivery assembly may be configured toautomatically deliver the distal end of the lead to the desired locationin the patient. Such a lead delivery system is disclosed in co-ownedU.S. patent application Ser. No. 14/846,578, filed Sep. 4, 2015, thedisclosure of which is incorporated herein by reference.

FIG. 7 is an illustration 700 of an exemplary process flow illustratinga method of delivering a lead having features consistent with thepresent disclosure. At 702, the location of blood-filled structures, inthe vicinity of an intercostal space, can be determined. The intercostalspace can be an intercostal space associated with the cardiac notch ofthe patient. Determining the location of the blood-filed structures maybe facilitated by one or more sensors configured to detect the locationof blood-filled structures.

At 704, a region can be chosen for advancing of a lead throughintercostal muscles associated with the cardiac notch. The region chosenmay be based on the determined location of blood-filled structures ofthe patient in that region. It is important that damage to blood-filledstructures, such as arteries, veins, and the like, is avoided whenadvancing a lead into a patient.

At 706, a lead can be advanced through the intercostal musclesassociated with the cardiac notch of the patient. Care should be takento avoid damaging important physiological structures. Sensors, of thekind described herein, may be used to help avoid damage to importantphysiological structures.

At 708, advancement of the lead through the intercostal muscles can beceased. Advancement may be ceased in response to an indication that thedistal end of the lead has advanced to the desired location. Indicationthat the distal end of the lead is at the desired location may beprovided through measurements obtained by one or more sensors of thekind described herein.

The lead advanced through the intercostal muscles associated with thecardiac notch of the patient can be configured to transmit therapeuticelectrical pulses to pace the patient's heart. FIG. 8A is anillustration 800 a of an exemplary lead 802 having features consistentwith the present disclosure. For the lead to deliver therapeuticelectrical pulses to the heart for pacing the heart, a proximal end 804of lead 802 is configured to couple with the pulse generator 102. Theproximal end 804 of lead 802 may be configured to couple with aconnection port 124. The connection port can be configured to couple theproximal end 804 of lead 802 to one or more conductors, such asconductors 118 and 120. When the proximal end 804 of lead 802 coupleswith connection port 124, a sealed housing may be formed between them.In some variations, the materials of connection port 124 and theproximal end 804 of lead 802 may be fused together. In some variations,the proximal end 804 of lead 802 may be configured to be pushed into thesealed housing 126, or vice versa. Optionally, the external diameter ofthe inserted member may be slightly greater than the internal diameterof the receiving member causing a snug, sealed fit between the twomembers. Optionally, a mechanism, such as a set-screw or mechanicallock, may be implemented upon the connection port 124 or proximal leadend 804 in order to prevent unintentional disconnection of the lead 802from pulse generator 102.

Also shown in FIG. 8A is the distal end 806 of lead 802. The distal end806 of lead 802 may comprise an electrode 808. In some variations, lead802 may include a plurality of electrodes. In such variations, lead 802may include a multiple-pole lead. Individual poles of the multiple-polelead can feed into separate electrodes. Electrode 808 at the distal end806 of lead 802 may be configured to deliver electrical pulses to pacethe heart when located in the desired position for pacing the heart.

The distal end 806 of lead 802 can include one or more sensors 810.Sensor(s) 810 can be configured to monitor physiological characteristicsof the patient while the distal end 806 of lead 802 is being advancedinto the patient. Sensors can be disposed along the length of lead 802.For example, sensor 812 is disposed some distance from the distal end806. Such sensors incorporated onto the lead can detect subtlephysiological, chemical and electrical differences that distinguish thelead's placement within the desired location, as opposed to otherlocations in the patient's thoracic cavity.

In some variations, the proximal end 804 of lead 802 may be coupled withpulse generator 102 prior to the distal end 806 of lead 802 beingadvanced through the intercostal space of the patient. In somevariations, the proximal end 804 of the lead 802 may be coupled withpulse generator 102 after the distal end 806 of lead 802 has beenadvanced to the desired location.

To assist in the placement of the lead, various medical instruments maybe used. The medical instruments may be used alone, or in combinationwith sensors disposed on the lead that is being placed. Medicalinstruments may be used to help the physician to access the desiredlocation for the placement of a lead and/or confirm that the distal endof the lead has reached the desired location. For example, instruments,such as an endoscope or laparoscopic camera, with its long, thin,flexible (or rigid) tube, light and video camera can assist thephysician in confirming that the distal end 806 of lead 802 has reachedthe desired location within the thoracic cavity. Other tools known toone skilled in the art such as a guidewire, guide catheter, or sheathmay be used in conjunction with medical instruments, such as thelaparoscopic camera, and may be advanced alongside and to the locationidentified by the medical instruments. Medical instruments such as aguidewire can be advanced directly to the desired location for thedistal end of the lead with the assistance of acoustic sound,ultrasound, real-time spectroscopic analysis of tissue, real-timedensity analysis of tissue or by delivery of contrast media that may beobserved by real-time imaging equipment.

In some variations, the patient may have medical devices previouslyimplanted that may include sensors configured to monitor physiologicalcharacteristics of the patient. The physiological characteristics of thepatient may change based on the advancement of the lead through theintercostal space of the patient. The previously implanted medicaldevice may have sensors configured to detect movement of the advancinglead. The previously implanted medical device can be configured tocommunicate this information back to the physician to verify thelocation of the advancing lead.

Sensors disposed on the lead, such as sensors 810 disposed on distal end806 of the lead may be used to facilitate the delivery of the lead tothe desired location. Sensor(s) 810 can be configured to facilitatedetermination of a depth of the distal end 806 of lead 802. As describedabove, the depth of the desired location within the patient can bedetermined using one or more medical instruments. This can be determinedduring implantation of the lead 802 or prior to the procedure takingplace.

Although sensor(s) 810 is illustrated as a single element in FIG. 8A,sensor(s) 810 can include multiple separate sensors. The sensors 810 canbe configured to facilitate placement of the distal end 806 of the lead802 at a desired location and verification thereof.

Sensor(s) 810 can be configured to transmit sensor information duringadvancement to the desired location. Sensor(s) 810 may transmit signalsassociated with the monitored physiological characteristics of thetissue within the vicinity of the distal end 806 of the lead 802. Insome variations, the signals from sensor(s) 810 may be transmitted to acomputing device(s) configured to facilitate placement of the lead 802in the desired location. In such variations, the computing device(s) canbe configured to assess the sensor information individually, or in theaggregate, to determine the location of the distal end 806 of lead 802.The computing device(s) can be configured to present alerts and/orinstructions associated with the position of the distal end 806 of lead802.

In some variations, lead 802 can be first coupled with connection port124 of pulse generator 102. Signals generated by sensor(s) 810 can betransmitted to a computing device(s) using transceiver 316 in pulsegenerator 102, as illustrated in FIG. 3.

An accelerometer may be used to facilitate delivery of the distal end806 of lead 802 to the desired location. An accelerometer may bedisposed at the distal end 806 of lead 802. The accelerometer may beconfigured to monitor the movement of the distal end 806 of lead 802.The accelerometer may transmit this information to a computing device orthe physician. The computing device, or the physician, can determine thelocation of the distal end 806 of the lead 802 based on the continuousmovement information received from the accelerometer as the lead 802 isadvanced into the patient. The computing device or the physician mayknow the initial entry position for lead 802. The movement informationcan indicate a continuous path taken by the lead 802 as it advanced intothe body of the patient, thereby providing an indication of the locationof the distal end 806 of lead 802. Pressure waves from the beating heartmay differ as absorption changes within deepening tissue planes. Thesepressure wave differences may be used to assess the depth of the distalend of the electrode.

The accelerometer can also be configured to monitor acoustic pressurewaves generated by various anatomical structures of the body. Forexample, the accelerometer can be configured to detect acoustic pressurewaves generated by the heart or by other anatomical structures of thebody. The closer the accelerometer gets to the heart, the greater theacoustic pressure waves generated by the heart will become. By comparingthe detected acoustical pressure waves with known models, a location ofthe distal end 806 of lead 802 can be determined.

Pressure waves or vibrations can be artificially generated to cause thepressure waves or vibrations to traverse through the patient. Thepressure waves or vibrations can be generated in a controlled manner.The pressure waves or vibrations may be distorted as they traversethrough the patient. The level of type of distortion that is likely tobe experienced by the pressure waves or vibrations may be known. Thepressure waves or vibrations detected by the accelerometer can becompared to the known models to facilitate determination or verificationof the location of the distal end 806 of lead 802.

Different tissues within a body exhibit different physiologicalcharacteristics. The same tissues situated at different locations withinthe body can also exhibit different physiological characteristics.Sensors, disposed on the distal end 806, of lead 802 can be used tomonitor the change in the physiological characteristics as the distalend 806 is advanced into the body of the patient. For example, thetissues of a patient through which a lead is advanced can demonstratediffering resistances, physiological properties, electrical impedance,temperature, pH levels, pressures, and the like. These differentphysiological characteristics, and the change in physiologicalcharacteristics, experienced as a sensor traverses through a body can beknown or identified. For example, even if the actual degree is not knownahead of time, the change in sensor input when the sensor traverses fromone tissue media to another may be identifiable in real-time.Consequently, sensors configured to detect physiological characteristicsof a patient can be employed to facilitate determining and verifying thelocation of the distal end 806 of lead 802.

Different tissues can exhibit different insulative properties. Theinsulative properties of tissues, or the change in insulative propertiesof tissues, between the desired entry-point for the lead and the desireddestination for the lead can be known. Sensor 810 can include anelectrical impedance detector. An electrical impedance detector can beconfigured to monitor the electrical impedance of the tissue in thevicinity of the distal end 806 of lead 802. The electrical impedance ofthe tissue monitored by the electrical impedance detector can becompared with the known insulative properties of the tissues between theentry point and the destination, to determine the location of the distalend of lead 802 or a transition from one tissue plane to another may berecognized by a measurable change in the measured impedance.

Varying levels of electrical activity can be experienced at differentlocations with the body. Electrical signals emitted from the heart, orother muscles can send electrical energy through the body. Thiselectrical energy will dissipate the further it gets from its source.Various tissues will distort the electrical energy in different ways.Sensors configured to detect the electrical energy generated by theheart and/or other anatomical structures can monitor the electricalenergy as the lead is advanced. By comparing the monitored electricalenergy with known models, a determination or verification of thelocation of the distal end 806 of lead 802 can be made. The sensors maybe configured to identify sudden changes in the electrical activitycaused by advancement of the sensor into different tissue planes.

Tissues throughout the body have varying pH levels. The pH levels oftissues can change with depth into the body. Sensor(s) 810 can include apH meter configured to detect the pH levels of the tissue in thevicinity of the sensor(s) 810 as the sensor(s) advance through thepatient. The detected pH levels, or detected changes in pH levels, canbe compared with known models to facilitate determination orverification of the location of the distal end 806 of lead 802. The pHmeter may be configured to identify sudden changes in the pH levelcaused by advancement of the meter into different tissue planes.

Different tissues can affect vibration-waves or sound-waves in differentways. Sensor(s) 810 can include acoustic sensors. The acoustic sensorscan be configured to detect vibration waves or sound waves travellingthrough tissues surrounding sensor(s) 810. The vibration waves can beemitted by vibration-emitting devices embedded the lead 802. Thevibration waves can be emitted by vibration-emitting devices located ona hospital gurney, positioned on the patient, or otherwise remote fromlead 802. Sensor(s) 810 can be configured to transmit detectedvibration-wave information to a computing device configured to determinethe location of the distal end 806 of lead 802 based on the detectedvibration-wave information.

Different tissues can have different known effects on the emittedelectromagnetic waves. Sensors can be used to detect the effect that thetissue in the vicinity of the sensors have on the electromagnet waves.By comparing the effect that the tissue has on the electromagnetic waveswith known electromagnetic effects, the identity of the tissue can beobtained and the location of the lead can be determined or verified. Forexample, sensor(s) 810 can include electromagnetic wave sensors.Electromagnetic wave sensors can include an electromagnetic wave emitterand an electromagnetic wave detector. The electromagnetic waves will beabsorbed, reflected, deflected, and/or otherwise affected by tissuesurrounding sensor(s) 810. Sensor(s) 810 can be configured to detect thechange in the reflected electromagnetic waves compared to the emittedelectromagnetic waves. By comparing the effect the tissue in thevicinity of the sensor(s) 810 has on the electromagnetic waves withknown models, a determination verification of the location of lead 802can be made. The sensors may be configured to identify sudden changes inthe electromagnetic activity caused by advancement of the sensor intodifferent tissue planes.

FIG. 9A is an illustration 900 of the distal end of an exemplarydelivery system 902 having features consistent with the presentlydescribed subject matter. While FIG. 9A is described with reference to adelivery system, one of ordinary skill in the art can appreciate andunderstand that the technology described herein could be applieddirectly to the end of a lead, such as lead 802. The present disclosureis intended to apply to a delivery system, such as delivery system 902,as well as a lead, such as lead 802.

Delivery system 902 can facilitate placement of the distal end of alead, such as lead 802 illustrated in FIG. 8, to a desired location byuse of electromagnetic waves, such as light waves. Delivery system 902may comprise a delivery catheter body 904. Delivery catheter body 904may be configured to facilitate advancement of delivery catheter body904 into the patient to a desired location. The distal tip 906 ofdelivery catheter body 904 may comprise a light source 908. Light source908 can be configured to emit photons having a visible wavelength,infrared wavelength, ultraviolet wavelength, and the like. Deliverycatheter body 904 may comprise a light detector 910. Light detector 910may be configured to detect light waves, emitted by the light source908, reflected by tissues surrounding distal tip 906 of deliverycatheter body 904.

FIG. 9B is an illustration 912 of an exemplary process for using thedelivery system illustrated in FIG. 9A. Light detector 910 can beconfigured to detect light waves reflected by the tissue adjacent thedistal end 906 of delivery system 902. Information associated with thedetected light waves may be transmitted to a computing device. Thecomputing device can be configured to interpret the informationtransmitted from light detector 910 and determine a difference betweenthe light emitted and the light detected.

At 914, light source 908 can be activated. Light source 908 may emitlight-waves into the tissue in the general direction of the intendedadvancement of delivery system 902. At 916, the tissue can absorb aportion of the emitted light waves. At 918, light detector 910 candetect the reflected light waves, reflected by tissues surrounding lightsource 908. At 920, a determination of a change in the absorption of thelight waves by tissues surrounding the distal tip 906 of delivery system902 can be made.

At 922, in response to an indication that the absorption of light waveshas not changed, delivery system 902 can be configured to advance adelivery system, such as delivery system 902, into the patient. In somevariations, a physician can advance delivery system 902 into thepatient. In other variations, the delivery system 902 can be advancedinto the patient automatically.

At 924, in response to an indication that the absorption of light waveshas changed, an alert can be provided to the physician. In somevariations, the alert can be provided to the physician through acomputing device configured to facilitate positioning of delivery system902 into the patient.

In some variations, a computing device may be configured to facilitatepositioning of delivery system 902 into the patient. The computingdevice can be configured to alert the physician to the type of tissue inthe vicinity of distal tip 906 of delivery system 902. In somevariations, the computing device can be configured to alert thephysician when the distal tip 906 reaches a tissue havingcharacteristics consistent with the desired location of the distal tip906 of delivery system 902. For example, when the characteristics of thetissue in the vicinity of the distal tip 906 match those within theintercostal tissues, or a particular location within the medistiunum, analert may be provided.

Blood vessels, both venous and arterial, absorb red, near infrared andinfrared (IR) light waves to a greater degree than surrounding tissues.When illuminating the surface of the body with red, near infrared andinfrared (IR) light waves, blood rich tissues, for example veins, willabsorb more of this light than other tissues, and other tissues willreflect more of this light than the blood rich tissues. Analysis of thepattern of reflections can enable the blood rich tissues to be located.A positive or negative image can be projected on the skin of the patientat the location of the vein. In some variations, the vein can berepresented by a bright area and the absence of a vein can berepresented as a dark area, or vice versa.

Delivery system 902 can include a subcutaneous visualization enhancer.The subcutaneous visualization enhancer may be configured to enhancevisualization of veins, arteries, and other subcutaneous structures ofthe body. The subcutaneous visualization enhancer can include movinglaser light sources to detect the presence of blood-filled structures,such as venous or arterial structures below the surface of the skin. Thesubcutaneous visualization enhancer can include systems configured toproject an image onto the surface of the skin that can show an operatorthe pattern of the detected subcutaneous blood-filled structures. Laserlight from laser light sources can be scanned over the surface of thebody using mirrors. A light detector can be configured to measure thereflections of the laser light and use the pattern of reflections toidentify the targeted blood rich structures.

Such subcutaneous visualization enhancers can be used to facilitatedetermination of the location for the initial approach for inserting alead, such as lead 802, through the intercostal space associated withthe cardiac notch of the patient. In some variations, the visualizationenhancers can be disposed remote from the delivery system and/or can beconfigured to enhance visualization enhancers disposed on the deliverysystem.

With the provision of a visualization of the detected subcutaneousstructures, the physician can assess the position of subcutaneousstructures such as the internal thoracic artery, or other structures, ofthe body while concurrently inserting components of the delivery systeminto the body, while avoiding those subcutaneous structures.

In some variations, during advancement of lead 802 through theintercostal space associated with the cardiac notch, sensor(s) 810 canbe configured to transmit obtained readings to a computing device forinterpretation. In some variations, the computing device is pulsegenerator 102. In some variations, pulse generator 102 is used totransmit the readings to an external computing device forinterpretation. In any event, the sensor information from the varioussensors can be used individually, or accumulatively, to determine thelocation of the distal end of lead 802.

FIG. 10 is a schematic illustration of a delivery control system 1000having features consistent with the current subject matter. The deliverycontrol system 1000 can be configured to automatically deliver a lead tothe desired position within the patient. For example, the deliverycontrol system 1000 can be configured to automatically deliver a distaltip of a lead through the intercostal space associated with the cardiacnotch.

Delivery control system 1000 can be configured to receive a plurality ofinputs. The inputs can come from one or more sensors disposed in, or on,the patient. For example, delivery control system 1000 can be configuredto receive subcutaneous structure visualization information 1002,information associated with delivery insertion systems 1004, informationassociated with sensors 1006, and the like.

Delivery control system 1000 can be configured to use remote sensors1006 to facilitate determination of the insertion site for the lead.Sensors 1006 can be disposed in various instruments configured to beinserted into the patient. Sensors 1006 can also be disposed in variousinstruments configured to remain external to the patient.

Delivery control system 1000 can be configured to perform depthassessments 1008. The depth assessments 1008 can be configured todetermine the depth of the distal end of an inserted instrument, such asa lead 802 illustrated in FIG. 8A. Depth assessments 1008 can beconfigured to determine the depth of the distal end of the insertedinstrument through light detection systems 1010, pressure wave analysis1012, acoustic analysis, and the like.

Depth assessments 1008 can be configured to determine the depth of thedelivery system, or lead, though pressure wave analysis systems 1012.Pressure waves can be detected by accelerometers as herein described.

Depth assessments 1008 can be configured to determine the depth of thedelivery system though acoustic analysis systems 1014. Acoustic analysissystem 1014 can be configured to operate in a similar manner to astethoscope. The acoustic analysis system 1014 can be configured todetect the first heart sound (S1), the second heart sound (S2), or otherheart sounds. Based on the measurements obtained by the acousticanalysis system 1014, a depth and/or location of the distal end of adelivery system and/or inserted medical component can be determined. Theacoustic analysis system 1014 can be configured to measure the duration,pitch, shape, and tonal quality of the heart sounds. By comparing theduration, pitch, shape, and tonal quality of the heart sounds with knownmodels, a determination or verification of the location of the lead canbe made. Sudden changes in the degree of heart sounds may be used toindicate advancement into a new tissue plane.

In some variations, the lead can include markers or sensors thatfacilitate the correct placement of the lead. Certain markers such as avisual scale, radiopaque, magnetic, ultrasound markers, and the like,can be position at defined areas along the length of the lead so thatthe markers can be readily observed by an implanting physician, orautomated system, on complementary imaging instruments such asfluoroscopy, x-ray, ultrasound, or other imaging instruments known inthe art. Through the use of these markers, the physician, or automatedimplantation device, can guide the lead to the desired location withinthe intercostal muscle, pleural space, mediastinum, or other desiredposition, as applicable.

Avoiding damage to tissues in the vicinity of the path-of-travel for thelead is important. Moving various tissues from the path of the leadwithout damaging them is also important. FIGS. 11A and 11B areillustrations 1100 and 1102 of an exemplary lead 802 having featuresconsistent with the present disclosure for moving and avoiding damage totissues during lead delivery. Lead 802 can comprise a distal tip 1104.Distal tip 1104 can include at least one electrode and/or sensor 1106.

Having leads directly touch the tissue of a patient can be undesirableand can damage the tissue. Consequently, the distal tip 1106 of lead 802can include an inflatable balloon 1108. Balloon 1108 can be inflatedwhen the distal tip 1106 of lead 802 encounters an anatomical structureobstructing its path, or prior to moving near sensitive anatomy duringlead delivery. The balloon may be configured to divert the obstacleand/or the lead to facilitate circumventing the anatomical structure ormay indicate that the lead has reached its intended destination.

To inflate the balloon, lead 802 can include a gas channel 1110. At theend of gas channel 1110 there can be a valve 1112. Valve 1112 can becontrolled through physical manipulation of a valve actuator, throughelectrical stimulation, through pressure changes in gas channel 1110and/or controlled in other ways. In some variations, the valve 1112 maybe configured at the proximal end of the lead 802.

When positioning lead 802 into a patient, lead 802 may cause damage to,or perforations of, the soft tissues of the patient. When lead 802 isbeing installed into a patient, distal tip 1104 of lead 802 canencounter soft tissue of the patient that should be avoided. In responseto encountering the soft tissue of the patient, gas can be introducedinto gas channel 1110, valve 1112 can be opened and balloon 1108 can beinflated, as shown in FIG. 11B. Inflating balloon 1108 can cause theballoon to stretch and push into the soft tissue of the patient, movingthe soft tissue out of the way and/or guiding distal tip 1104 of lead802 around the soft tissue. When distal tip 1104 of lead 802 has passedby the soft tissue obstruction, valve 1112 can be closed and the balloondeflated.

In some variations, a delivery component or system is used to facilitatedelivery of a lead, such as lead 802, to the desired location. FIG. 12is an illustration 1200 of an exemplary delivery system for a leadhaving features consistent with the present disclosure. An example ofthe delivery system is an expandable sheath 1202. Expandable sheath 1202can be inserted into the patient at the desired insertion point,identified using one or more of the technologies described herein.Expandable sheath 1202 can include a tip 1204. In some variations, tip1204 may be radiopaque. A radiopaque tip 1204 may be configured tofacilitate feeding of the expandable sheath 1202 to a desired locationusing one or more radiography techniques known in the art and describedherein. Such radiography techniques can include fluoroscopy, CT scan,and the like.

Tip 1204 can include one or more sensors for facilitating the placementof the lead. The sensors included in tip 1204 of the expandable sheath1202 can be the same or similar to the sensors described herein formonitoring physiological characteristics of the body and othercharacteristics for facilitating positioning of a lead in a body.

Expandable sheath 1202 can include a channel 1206 running through ahollow cylinder 1208 of expandable sheath 1202. When tip 1204 ofexpandable sheath 1202 is at the desired location, gas or liquid can beintroduced into hollow cylinder 1208. The gas or liquid can beintroduced into hollow cylinder 1208 through a first port 1210. Hollowcylinder 1208 can expand, under the pressure of the gas or liquid,causing channel 1206 running through hollow cylinder 1208 to increase insize. A lead, such as lead 802 illustrated in FIG. 8A, can be insertedinto channel 1206 through a central port 1212. Hollow cylinder 1208 canbe expanded until channel 1206 is larger than the lead. In somevariations, channel 1206 can be expanded to accommodate leads of severalFrench sizes. Once the lead is in the desired place, expandable sheath1202 can be removed, by allowing the lead to pass through channel 1206.In some variations, liquid or gas can be introduced into or removed fromchannel 1006 through a second port 1214.

Using expandable sheath 1202 can provide an insertion diameter smallerthan the useable diameter. This can facilitate a reduction in the riskof damage to tissues and vessels within the patient when placing thelead.

When electricity is brought within the vicinity of muscle tissue, themuscle will contract. Consequently, having a lead for carryingelectrical pulses traversing through intercostal muscle tissue may causethe intercostal muscle tissue to contract. Electrical insulation can beprovided in the form of a receptacle disposed in the intercostal muscle,where the receptacle is configured to electrically insulate theintercostal muscle from the lead.

FIG. 13 is an illustration 1300 of an intercostal space 1302 associatedwith the cardiac notch of the left lung with an exemplary leadreceptacle 1304 having features consistent with the present disclosure.Lead receptacle 1304 can facilitate the placement of leads, and/or otherinstruments and avoid the leads and/or instruments physically contactingthe intercostal tissue. When the distal end of the lead is positioned toterminate in the intercostal muscle, the lead can be passed through leadreceptacle 1304 that has been previously placed within the patient'sintercostal muscles. Lead receptacle 1304 can be configured to beelectrically insulated so that electrical energy emanating from the leadwill not stimulate the surrounding intercostal and skeletal muscletissue, but will allow the electrical energy to traverse through andstimulate cardiac tissue.

The intercostal space 1302 is the space between two ribs, for example,rib 1306 a and rib 1306 b. Intercostal muscles 1308 a, 1308 b and 1308 ccan extend between two ribs 1306 a and 1306 b, filling intercostal space1302. Various blood vessels and nerves can run between the differentlayers of intercostal muscles. For example, intercostal vein 1310,intercostal artery 1312, the intercostal nerve 1314 can be disposedunder a flange 1316 of upper rib 1306 a and between the innermostintercostal muscle 1308 c and its adjacent intercostal muscle 1308 b.Similarly, collateral branches 1318 can be disposed between theinnermost intercostal muscle 1308 c and its adjacent intercostal muscle1308 b.

The endothoracic facia 1320 can abut the inner-most intercostal muscle1308 c and separate the intercostal muscles from the parietal pleura1322. The pleural cavity 1324 can be disposed between the parital pleura1322 and the visceral pleura 1326. The visceral pleura 1326 can abut thelung 1328.

FIG. 14 is an illustration 1400 of an exemplary lead fixation receptacle1304 illustrated in FIG. 13, having features consistent with the presentdisclosure.

Lead receptacle 1304 may comprise a cylindrical body, or lumen 1328,from an outer side of an outermost intercostal muscle to an inner sideof an innermost intercostal muscle of an intercostal space. Lumen 1328may be configured to support a lead traversing through it. Lumen 1328may comprise an electrically insulating material configured to inhibittraversal of electrical signals through walls of lumen 1328. In somevariations, end 1336 of the receptacle 1304 may pass through theinnermost intercostal muscle 1308 c. In some variations, end 1338 ofreceptacle 1304 can pass through outermost intercostal muscle 1308 a.

Lumen 1328 can terminate adjacent the pleural space 1324. In somevariations, the lumen 1328 can terminate in the mediastinum. In somevariations, receptacle 1304 can be configured to be screwed into theintercostal muscles 1308 a, 1308 b, and 1308 c. Receptacle 1304 can alsobe configured to be pushed into the intercostal muscles 1308 a, 1308 band 1308 c.

Lead receptacle 1304 may include a fixation flange 1330 a. Fixationflange 1330 a may be disposed on the proximal end of the lumen 1328 andconfigured to abut the outermost intercostal muscle 1308 a. Leadreceptacle 1304 may include a fixation flange 1330 b. Fixation flange1330 b can be disposed on the distal end of the lumen 1328 andconfigured to abut the outermost intercostal muscle 1308 c. Leadreceptacle 1304 can be implanted into the intercostal muscles 1308 a,1308 b, and 1308 c by making an incision in the intercostal muscles 1308a, 1308 b, and 1308 c, stretching the opening and positioning leadreceptacle 1304 into the incision, taking care to ensure that theincision remains smaller than the outer diameter of flanges 1330 a and1330 b. In some variations flanges 1330 a and 1330 b can be configuredto be retractable allowing for removal and replacement of the leadfixation receptacle 1304.

Lead receptacle 1304 can be fixed in place by using just flanges 1330 aand 1330 b. Lead receptacle 1304 may also be fixed in place by using aplurality of surgical thread eyelets 1332. Surgical thread eyelets 1332can be configured to facilitate stitching lead receptacle 1304 to theintercostal muscles 1308 a and 1308 c to fix lead receptacle 1304 inplace.

Receptacle 1304 can include an internal passage 1334. Internal passage1334 can be configured to receive one or more leads and facilitate theirtraversal through the intercostal space 1302.

Lead receptacle 1304 can be formed from an electrically insulatingmaterial. The electrically insulating material can electrically isolatethe intercostal muscles 1308 a, 1308 b and 1308 c from the leadstraversing through lead receptacle 1304.

Lead receptacle 1304 can be formed from materials that are insulative.The material can include certain pharmacological agents. For example,antibiotic agents, immunosuppressive agents to avoid rejection of leadreceptacle 1304 after implantation, and the like. In some variations,lead receptacle 1304 can be comprised of an insulative polymer coated orinfused with an analgesic. In some variations, the lead receptacle 1304can be comprised of an insulative polymer coated or infused with ananti-inflammatory agent. The polymer can be coated or infused with otherpharmacological agents known to one skilled in the art to treat acuteadverse effects from the implantation procedure or chronic adverseeffects from the chronic implantation of the lead or receptacle withinthe thoracic cavity.

FIG. 15 is an illustration of lead receptacle 1304 having featuresconsistent with the present disclosure. Lead fixation receptacle cancomprise a septum 1340, or multiple septums disposed traversely withinlumen 1338. Septum 1340 can be selectively permeable such that when alead is inserted through septum 1340, septum 1340 can be configured toform a seal around the lead traversing through lumen 1338 to prevent theingress or egress of gas, fluid, other materials, and the like, throughlumen 1338. Septum 1340 may optionally permit the egress of certain gasand fluid but prevent ingress of such materials through lumen 1338.

In some variations, the lead receptacle can comprise multiple lumens.For example, lead receptacle can comprise a second lumen configured totraverse from an outermost side of an outermost intercostal muscle to aninnermost side of an innermost intercostal muscle. Second lumen can beconfigured to facilitate dispensing of pharmacological agents into thethorax of the patient.

The lumens for such a lead receptacle can be used for differing purposesin addition to the passage of a single lead into the pleural space ormediastinum. The multiple lumens can provide access for multiple leadsto be passed into the pleural space or mediastinum.

FIG. 16 is an illustration of an exemplary lead fixation receptacle 1342having features consistent with the present disclosure. Lead fixationreceptacle 1342 can include a first lumen 1344, similar to lumen 1338 ofthe lead receptacle 1304 illustrated in FIGS. 14 and 15. Lead fixationreceptacle 1342 can include an additional lumen 1346. Additional lumen1346 can be provided as a port to provide access to the thoracic cavityof the patient. Access can be provided to facilitate dispensing ofpharmacological agents, such as pharmacological agents to treat variousadverse effects such as infection or pain in the area surrounding leadreceptacle 1342, pleural space, mediastinum, and/or other areassurrounding the thoracic cavity of the patient. Additional lumen 1346can provide access for treatment of other diseases or disordersaffecting organs or other anatomical elements within the thoraciccavity. For example, additional lumen 1346 can facilitate the evacuationof gas or fluid from the thorax, and the like.

The lead receptacle as described with reference to FIGS. 13-16 can befixated to cartilage, or bone within the thoracic cavity. In somevariations, the lead receptacle can be configured to be disposed betweenthe intercostal muscles and a rib, thereby potentially reducing damageto the intercostal muscles caused by its insertion. The lead receptaclecan be in passive contact with tissue surrounding the cardiac notch. Forexample, the lead receptacle can abut the superficial facia on theoutermost side and the endothoracic facia or the parietal pleura on theinnermost side.

In some variations, the lead receptacle can be actively fixed intoposition using one end of the lead receptacle. For example, only oneflange can include surgical thread holes to facilitate sewing of theflange into the intercostal muscles.

Active fixation, whether at flanges, or along the lumen of the leadfixation receptacle, can include, for example, the use of tines, hooks,springs, screws, flared wings, flanges and the like. Screws can be usedto screw the lead fixation receptacle into bone or more solid tissueswithin the thoracic cavity. Hooks, tines, springs, and the like, can beused to fix the lead fixation receptacle into soft tissues within thethoracic cavity.

In some variations the lead receptacle can be configured to facilitatein-growth of tissue into the material of which the lead fixationreceptacle is comprised. For example, the lead fixation receptacle canbe configured such that bone, cartilage, intercostal muscle tissue, orthe like, can readily grow into pockets or fissures within the surfaceof the lead receptacle. Facilitating the growth of tissue into thematerial of the lead receptacle can facilitate fixation of thereceptacle.

In some variations, the receptacle can be configured to actively fixbetween layers of the intercostal muscle. With reference to FIG. 13, thelayered nature of the intercostal muscle layers 1308 a, 1308 b and 1308c can be used to facilitate fixation of the lead receptacle into theintercostal space. For example, flanges can be provided that extendbetween the intercostal muscle layers. Incisions can be made at off-setpositions at each layer of intercostal muscle such that when the leadreceptacle is inserted through the incisions, the intercostal musclesapply a transverse pressure to the lead receptacle keeping it in place.For example, a first incision can be made in the first intercostalmuscle layer 1308 a, a second incision can be made in the secondintercostal muscle layer 1308 b, offset from the first incision, and athird incision can be made to the third intercostal muscle layer 1308 cin-line with the first incision. Inserting the lead receptacle throughthe incisions, such that the lead receptacle is situated through allthree incisions, will cause the second intercostal muscle layer 1308 bto apply a transverse pressure to the lead receptacle that is counteredby the first intercostal muscle layer 1308 a and the third intercostalmuscle layer 1308 c, facilitating keeping the lead receptacle in place.

A pulse generator, such as pulse generator 102 illustrated in FIG. 1,can be configured to monitor physiological characteristics and physicalmovements of the patient. Monitoring can be accomplished through sensorsdisposed on, or in, the pulse generator, and/or through sensors disposedon one or more leads disposed within the body of the patient. The pulsegenerator can be configured to monitor physiological characteristics andphysical movements of the patient to properly detect heart arrhythmias,dyssynchrony, and the like.

Sensor(s) can be configured to detect an activity of the patient. Suchactivity sensors can be contained within or on the housing of the pulsegenerator, such as pulse generator 102 illustrated in FIG. 1. Activitysensors can comprise one or more accelerometers, gyroscopes, positionsensors, and/or other sensors, such as location-based technology, andthe like. Sensor information measured by the activity sensors can becross-checked with activity information measured by any concomitantdevices.

In some variations, an activity sensor can include an accelerometer. Theaccelerometer can be configured to detect accelerations in any directionin space. Acceleration information can be used to identify potentialnoise in signals detected by other sensor(s), such as sensor(s)configured to monitor the physiological characteristics of the patient,and the like, and/or confirm the detection of signals indicatingphysiological issues, such as arrhythmias or other patient conditions.

In some variations, a lead, such as lead 802 in FIG. 8, can beconfigured to include sensors that are purposed solely for monitoringthe patient's activity. Such sensors may not be configured to provideadditional assistance during the implantation procedure. These sensorscan include pulmonary, respiratory, minute ventilation, accelerometer,hemodynamic, and/or other sensors. Those sensors known in the art thatare used to real-time, or periodically monitor a patient's cardiacactivity can be provided in the leads. These sensors are purposed toallow the implanted device to sense, record and in certain instances,communicate the sensed data from these sensors to the patient'sphysician. In alternative embodiments, the implanted medical device mayalter the programmed therapy regimen of the implanted medical devicebased upon the activity from the sensors.

In some variations, sensors, such as sensors 810 and 812 of FIG. 8A, maybe configured to detect the condition of various organs and/or systemsof the patient. Sensor(s) 810, 812 can be configured to detect movementof the patient to discount false readings from the various organs and/orsystems. Sensor(s) 810, 812 can be configured to monitor patientactivity. Having a distal end 806 of lead 802 positioned in the cardiacnotch abutting the parietal pleura, sensor(s) 810, 812 can collectinformation associated with the organs and/or systems of the patient inthat area, for example the lungs, the heart, esophagus, arteries, veinsand other organs and/or systems. Sensor(s) 810 can include sensors todetect cardiac ECG, pulmonary function, sensors to detect respiratoryfunction, sensors to determine minute ventilation, hemodynamic sensorsand/or other sensors. Sensors can be configured independently to monitorseveral organs or systems and/or configured to monitor severalcharacteristics of a single organ simultaneously. For example, using afirst sensor pair, the implanted cardiac pacing system may be configuredto monitor the cardiac ECG signal from the atria, while simultaneously,a second sensor pair is configured to monitor the cardiac ECG signalfrom the ventricles.

A lead disposed in the body of a patient, such as lead 802 of FIG. 8A,can include sensors at other areas along the lead, for example, sensors812. The location of sensors 812 along lead 802 can be chosen based onproximity to organs, systems, and/or other physiological elements of thepatient. The location of sensors 812 can be chosen based on proximity toother elements of the implanted cardiac pacing system.

Additional leads may be used to facilitate an increase in the sensingcapabilities of the implantable medical device. In one embodiment, inaddition to at least one lead disposed within the intercostal muscle,pleural space or mediastinum, another lead is positioned subcutaneouslyand electrically connected to the implantable medical device. Thesubcutaneously placed lead can be configured to enhance the implantablemedical device's ability to sense and analyze far-field signal's emittedby the patient's heart. In particular, the subcutaneous lead enhancesthe implantable medical device's ability to distinguish signals fromparticular chambers of the heart, and therefore, appropriatelycoordinate the timing of the required pacing therapy delivered by theimplantable medical device.

Additional leads in communication with the implantable medical device orpulse generator, and/or computing device, can be placed in other areaswithin the thoracic cavity in order to enhance the sensing activity ofthe heart, and to better coordinate the timing of the required pacingtherapy delivered by the implantable medical device. In certainembodiments, these additional leads are physically attached to theimplantable medical device of the present disclosure.

The leads used to deliver therapeutic electrical pulses to pace theheart can comprise multiple poles. Each pole of the lead can beconfigured to deliver therapeutic electrical pulses and/or obtainsensing information. The different leads can be configured to providedifferent therapies and/or obtain different sensing information. Havingmultiple sensors at multiple locations can increase the sensitivity andeffectiveness of the provided therapy.

FIG. 8B is an illustration 800 b of an exemplary lead 802 havingfeatures consistent with the present disclosure. In some variations,lead 802 can comprise a yoke 816. The yoke can be configured to maintaina hermetically sealed housing for the internal electrical cables of lead802, while facilitating splitting of the internal electrical cables intoseparate end-leads 818 a, 818 b, 818 c. Yoke 816 can be disposed towarddistal end of lead 802. While three end-leads 818 a, 818 b, 818 c areillustrated in FIG. 8B, the current disclosure contemplates fewerend-leads as well as a greater number of end-leads emanating from yoke816.

The different end-leads 818 a, 818 b, 818 c, can include differentelectrodes and/or sensors. For example, end-lead 818 b can include anelectrode 808 b at the distal end 806 b of end-lead 818 b that differsfrom electrode 808 a at distal end 806 a of end-lead 818 a. Electrode808 b can have flanges 820. Flanges 820 can be configured to act as ananchor, securing the distal end 806 b of end-lead 818 b in positionwithin the patient. Electrode 808 b with flanges 820 can be suitable foranchoring into high-motion areas of the body where end-lead 818 b wouldotherwise move away from the desired location without the anchoringeffect provided by flanges 820. Similarly, electrode 808 c at the distalend 806 c of end-lead 818 c can be configured for a different functioncompared to the electrodes at the end of other end-leads.

Lead 802 can be a multi-pole lead. Each pole can be electronicallyisolated from the other poles. The lead 802 can include multipleisolated poles, or electrodes, along its length. The individual polescan be selectively activated. The poles may include sensors formonitoring cardiac or other physiological conditions of the patient, orelectrodes for deliver therapy to the patient.

The sensing characteristics of a patient can change over time, or canchange based on a patient's posture, a multi-pole lead permits theimplantable medical device facilitate monitoring a patient's statethrough multiple sensing devices, without requiring intervention toreposition a lead. Furthermore, a multi-pole lead can be configured tofacilitate supplementary sensing and therapy delivery vectors, such assensing or stimulating from one pole to a plurality of poles, sensing orstimulating from a plurality of poles to a single pole, or sensing orstimulating between a plurality of poles to a separate plurality ofpoles. For example, should one particular vector be ineffective attreating a particular arrhythmia, the implantable medical device, orpulse generator, can be configured to switch vectors between the poleson the lead and reattempt therapy delivery using this alternativevector. This vector switching is applicable for sensing. Sensingcharacteristics can be monitored, and if a sensing vector becomesineffective at providing adequate sensing signals, the implantablemedical device can be configured to switch vectors or use a combinationof one or more sensor pairs to create a new sensing signal.

In some variations, at yoke 816, each of the poles of the multi-polelead can be split into their separate poles. Each of the end-leadsemanating from the yoke 816 can be associated with a different pole ofthe multi-pole lead.

Some of the end-leads emanating from yoke 816 can be configured forproviding sensor capabilities of and/or therapeutic capabilities to thepatient's heart. Others of the end-leads emanating from yoke 816 can beconfigured to provide sensor capabilities and/or therapeuticcapabilities that are unrelated to the heart. Similarly, the cardiacpacing system herein described can include leads 802, or medical leads,that provide functionality unrelated to the heart.

In some variations, the lead can be bifurcated. A bifurcated lead cancomprise two cores within the same lead. In some variations, thedifferent cores of the bifurcated lead can be biased to bend in apredetermined manner and direction upon reaching a cavity. Such a cavitycan, for example, be the mediastinum. Bifurcated lead cores can becomprised of shape memory materials, for example, nitinol or othermaterial known in the art to deflect in a predetermined manner uponcertain conditions. The conditions under which the bifurcated lead coreswill deflect include electrical stimulation, pressure, temperature, orother conditions. In some variations, each core of the bifurcated leadcan be configured so that it is steerable by the physician, or anautomated system, to facilitate independent advancement of each core ofthe bifurcated lead, in different directions.

A pacemaker of the kinds contemplated by the present disclosure cancomprise one or more sensors configured to monitor the activity of theatrial or ventricular chambers of the patient's heart, methods to filterand prepare these sensor signals for use by downstream algorithms,methods to trigger heartbeat detections or detections of otherphysiologic activity from these signals, methods to authenticate theaccuracy of such cardiac or physiologic detections and methods toprepare for, and control pacing therapy.

FIGS. 17A and 17B are illustrations showing an exemplary data flow 1700for sensing signals and signal preparation for cardiac therapy havingfeatures consistent with the current subject matter. Data flow 1700 canbe employed by a cardiac pacing system, such as the cardiac pacingsystems described herein. The cardiac pacing system can include apacemaker, such as pulse generator 102 illustrated in FIG. 1, pacingleads, such as leads 802 illustrated in FIG. 8, and/or other components.The cardiac pacing system can include sensor leads having one or moresensors configured to monitor physiological characteristics of thepatient. Sensing leads disposed in or adjacent to the cardiac notch ofthe patient can be effective at monitoring the physiologicalcharacteristics in the vicinity of the cardiac notch such as thepatient's electrocardiogram, respiration, blood oximetry, temperature,and the like. Sensing leads that include an accelerometer can be used todetect the patient's posture, the functioning of the cardiac or skeletalmuscles and other physical characteristics monitored by anaccelerometer.

A cardiac pacing system can comprise a pulse generator configured tomonitor physiological characteristics of a patient. The pulse generatorcan deliver therapeutic electrical pulses through an electrode toregulate a heartbeat of a patient in response to certain conditionsbeing detected in the monitored physiological characteristics of apatient. To monitor the physiological characteristics of a patient, asensor(s) can be provided in the patient, from which the pulse generatorcan receive information associated with the physiologicalcharacteristics of the patient. However, the sensors not only obtainmeasurements associated with physiological characteristics of thepatient, the sensors also capture noise from exogenous or endogenoussources and signals unrelated to the monitored physiologicalcharacteristics. Consequently, the pulse generator can be configured tofilter out, or normalize, the noise and signals.

Signal preparation 1702 prepares the sensing signals for use by thedownstream system/algorithms. This stage is primarily focused on thesignals used for sensing, not the vector used for pacing. The signalpreparation stage 1702 can take all of the available input signals 1704from the system (e.g., ECG pairs, respiration, blood oximetry, etc.),apply filters to these signals 1706, identify noise contained withinthese signals, determine which signals are acceptable for use and thenselect the preferred signals for downstream sensing algorithms. Thesignal preparation stage can continually monitor all of the signals todetermine if changes to the selected signal are required.

There are many sources of noise that can interfere with the quality ofthe signal being sensed by the cardiac pacing system. For example, noisecan be generated from the patient's own muscle tissue. When a patientflexes a muscle, signals caused by, for example, electrical waves,pressure waves, temperature changes, and the like, can be detected bythe sensors associated with a cardiac pacing system. Another example ofnoise that can cause a distortion in the signals being received by thecardiac pacing system is radio frequency interference. Radio frequencyinterference can come from the components of the cardiac pacing systemitself, from other components within the body, from external sourcessuch as cell phones, electrical cables, and the like. The effect ofthese signals, or noise, can be accounted for by filtering.

The cardiac pacing system, configured to monitor the patient's heart,can include hardware filters 1710, software filters 1712 and gainamplifiers 1714 for filtering out the noise or interference signals 1706detected by sensors of the cardiac pacing system. The filtering 1706 canbe applied in series or become a product of multiple parallel processesto yield a useable signal for downstream operations.

Hardware filters 1710 are fixed filters within the hardware of thecardiac pacing system. Hardware filters 1710 are designed to removenoise and apply a basic set of filtering in preparation for theoperations of the software filters 1712. Hardware filters 1710 can beconfigured to cancel out or account for signals not generated from thepatient's heart using hardware filtering solutions. In some variations,the cardiac pacing system can use a fixed hardware low-pass filter, afixed high-pass filter, a notch filter and the like. In some variations,the cardiac pacing system can use a series of hardware filters 1710 tocreate a desired band-pass filter response. Some filter typescontemplated include Butterworth, Chebyshev, and the like.

Multiple hardware filter band-pass filter ranges can be used to filterdifferent signals for the cardiac pacing system. For example, a hardwarefilter can be included as a band-pass filter for ECG signals from 5 Hzto 25 Hz and respiration rate signal from 0.001 Hz to 0.1 Hz.

Hardware filters 1710 can be disposed in the signal path of a sensor(s).For example, hardware filters 1710 can be disposed in a lead of thecardiac pacing system, at a port for one or more conductors of a pulsegenerator, or the like.

A cardiac pacing system can include software filters 1712. Softwarefilters 1712 can be configured to account for exogenous signals usingsoftware filtering solutions. Software filters 1712 can be modifiable byfirmware/software to be applied to one or more sensed signals 1704.Examples of modifiable software filters include a permanent digitalfilter 1716 that is controllable via the programmer, a dynamic filter1718 which is automatically adjusted based upon certain criteria and anactive baseline algorithm 1720 to ensure the sensing signal remainscentered about the “zero” baseline.

Software filters 1712 can be executed by one or more processors of thecardiac pacing system, such as being embodied in controller 302 of pulsegenerator 102 illustrated in FIG. 3. Software filters 1712 can beexecuted by one or more processors of a programmer, such as programmer320 illustrated in FIG. 3.

A digital filter 1716 is a modifiable, digital software filter 1712 thatcan be applied to sensing channels used by the cardiac pacing system.Because the cardiac pacing system can sense numerous physiologic signals(e.g., ECG, respiration, pulse oximetry), the signal inputs 1704 foreach of the physiologic signals can vary. A digital filter 1716 can beused in combination with hardware filters 1710 to refine desiredbandpass settings. For example, the cardiac pacing system's fixedhardware filters 1710 may be applied to an ECG input channel using a 3Hz to 30 Hz bandpass. Following the hardware filters 1710, a digitalfilter 1716 may subsequently refine the signal further to 9 Hz to 24 Hz.

A digital filter 1716 can be programmed to modify its filtering uponmeeting certain conditions. For example, when additional data iscollected by the cardiac pacing system suggesting a bandpass setting maybe too broad and should be narrowed, upon reaching such determination,the digital filter 1716 can be reprogrammed to adjust the bandpasssetting accordingly. Such reprogramming can be executed by the physicianusing one or more processors controlled by the programmer 320, orautomatically by the cardiac pacing system.

Modifications to a digital filter 1716 can be made based on otherunrelated signals sensed by the cardiac pacing system. For example, uponsensing an increased respiratory rate by one sensing channel, thedigital filter 1716 for an independent ECG sensing channel can beautomatically adjusted to refine the bandpass settings, and thesubsequent data, being collected during the time of increasedrespiratory rate. Similarly, when the respiratory rate returns tonormal, the digital filter 1716 for the ECG sensing channel can returnto its original bandpass setting. Similar modifications can be made inresponse to posture changes, heart rate or the like.

Software filters 1712 can be configured to dynamically filter noisesignals. FIG. 17B is an illustration of an exemplary process flow fordynamic filtering 1718 of signals, having features consistent with thepresent disclosure.

In FIG. 17B at 1718, the incoming signal(s) can be dynamically filtered.Dynamic filtering 1718 can be configured to allow the cardiac pacingsystem to monitor sensed input signals and automatically apply asecondary digital filter profile 1730, as needed, based upon theassessment of certain criteria from such input signals. The secondarydigital filter 1730 can be layered into the sensing architecture so thatthe secondary digital filter 1730 can be utilized, or deactivated,without affecting the permanent digital filter 1716. Dynamic filteringcan provide more timely changes to the cardiac pacing system's sensingarchitecture for specific known events and based on assessment ofcertain criteria.

The filtered signal is assessed and processed based on one or morecriteria 1732. The set of criteria 1732 being assessed include changesin signal amplitude, heart rate, posture, transthoracic impedance,ventricular pacing, ventricular sensing, atrial pacing, atrial sensing,morphology, frequency analysis on the template of the sensed signal,noise, states of the implanted pulse generator, and the like. Morphologyassessments can include assessing monophasic or biphasic characteristicsof the cardiac signal, such as narrow vs. wide signal complexes,patterns of peaks and nadirs and timing between particular signalcharacteristics on one or more input signals. States of the implantedpulse generator include storage mode prior to implant, set up mode atthe time of implant, follow-up mode while communicating with theprogrammer, explant mode while surgically removing the cardiac pacingsystem, or other protective states that may be utilized in the presenceof surgical procedures such as electrocautery, ultrasound, MRI or thelike.

At 1734, a determination is made as to whether the signal meets the oneor more criteria being assessed 1732. In response to a determinationthat the signal does not meet the criteria, no additional filter changesare required, and the signal is ready to be passed to downstreamalgorithms. At 1736, in response to a determination that the signal doesmeet the criteria, a determination can be made as to whether to alterthe dynamic filter response. In response to a determination that thebandpass frequency should be altered, at 1738, the filter frequencyresponse can be changed and the signals are then reprocessed through themodified filter. In response to a determination that the bandpassfrequency should not be altered, the signals are then presented to thecardiac pacing system's downstream algorithms for processing.

Dynamically filtering 1718 can be initiated during certain testingregiments performed by the programmer, such as programmer 320illustrated in FIG. 3. Such testing regiments can be performed followingthe implant procedure or in connection with certain follow-up testing.For example, a physician can apply certain dynamic filtering assessmentswhen obtaining patient input during the setup procedure. Obtaining suchuser input can facilitate the normalization process for the cardiacpacing system, especially when conducting, for example, postureanalysis, exercising, and the like.

An alternative example where the programmer initiates a dynamicfiltering assessment is within a noisy environment. Radio frequencycommunication can introduce noise in the environment affectingcommunication between various elements of the cardiac pacing system.Sensors within the programmer and/or the cardiac pacing system canidentify a high degree of radio frequency noise in the environment andtemporarily activate the second dynamic filter 1730 during thecommunication session with the programmer. Consequently, the cardiacpacing system can modify the distorted signals through dynamic filtering1718 to allow the intended testing within the noisy environment.

Dynamic filtering 1718 can be initiated by the cardiac pacing systembased on changes in the physiological characteristics of the patient andthe patient's environment. For example, if the patient's heart rateincreases, the bandpass filter frequency may be narrowed temporarily byactivating a second digital filter 1730 to ensure T-waves are filteredmore aggressively. Such dynamic filtering adjustments can avoidover-detection of sensed signals. Similarly, if a patient works in anenvironment producing a high degree of noise (e.g., welder,electrician), dynamic filtering 1718 can temporarily filter the dominantfrequency of the environmental noise and avoid the potential foroverlying noise or saturation of sensed signals. Preventing saturationenables the cardiac pacing system to avoid missing critical indicatorsof heart arrhythmias, dyssynchrony, and the like.

A baseline reference value (or “baseline”) is a representation of zeroinput on a sensing channel. With no input on a sensing channel, thesignal will come to rest at the baseline value. Deflections from thisbaseline occur in response to measured input from the patient. Forexample, as the heart beats, a P-wave, QRS and T-wave are noted on theECG. These waves are noted as voltage departures from the signalbaseline on the ECG sensing channel. For proper sensing operation, it isimportant that the signal baseline be maintained at the zero input levelsuch that any measurements from a sensor are accurately represented asan electrical delta from zero. Should the baseline of the signal wanderaway from zero, the sensing algorithms can be misled leading toinadvertent therapeutic response. Exogenous noise or patient movementcan cause the baseline signal to shift even though the patient isperfectly normal and does not require therapeutic pacing treatment.Software filters 1712 and algorithmic processes can be configured toaccount for such baseline shifts, distinguish between treatable andnon-treatable rhythms, and establish new temporary baselines in thesecircumstances.

The active baseline algorithm 1720 initiates temporary and remedialactions to maintain or reestablish a proper sensing baseline upon aunique baseline-shifting event. The active baseline algorithm 1720 isthen deactivated upon correction of the baseline. For example, adefibrillation shock can cause the sensing inputs of the cardiac pacingsystem to become saturated and could inappropriately trigger heartbeatdetections. This in turn could cause an inappropriate inhibition ofpacing therapy delivery. The active baseline algorithm 1720 canrecognize the temporary signal saturation as a defibrillation shock. Toremediate the event, the active baseline algorithm 1720 can temporarilyapply more aggressive filtering and algorithmic mechanisms toreestablish an appropriate baseline allowing the cardiac pacing systemto make appropriate decisions based on the correct baseline signal.

In certain situations, the cardiac pacing system and the deviceproducing the defibrillation (ICD) are in active communication withanother. When notified by the ICD of a pending shock with or withoutpost-shock pacing by the ICD, the active baseline algorithm 1720 canprophylactically condition the cardiac pacing system's sensing filtersand algorithms accordingly. The resultant sensing signals following theshock will therefore maintain a proper sensing baseline and areacceptable for downstream system evaluation.

In addition to reestablishing a proper baseline following adefibrillation shock, the active baseline algorithm 1720 can temporarilyalter the pacing mode of the cardiac pacing system. The heart rate canbe monitored by various sensors on various leads in communication withthe cardiac pacing system. Hardware and software filters can beconfigured to update the dynamic baseline algorithm 1720, or their levelof filtering, based on the detected heart rate. Such dynamicmodifications enable the cardiac pacing system to utilize an increasedpacing rate or higher pacing output in a post-shock manner. For example,the active baseline algorithm 1720 can temporarily cause the cardiacpacing system to switch from a VDD mode with 50 ppm, 3.0V @ 1.0 ms to aVVI mode with 75 ppm, max output for 30 seconds.

Baseline reestablishment by the active baseline algorithm 1720 can be arepetitive process. For example, shortly after a defibrillation shockand more aggressive filter application, the sensors may continue to failto provide meaningful readings. The active baseline algorithm 1720 canrepeatedly cause the cardiac pacing system to refine filters or generatenew filter schemes to cause the sensors to function properly and providethe desired information.

The active baseline algorithm 1720 can be updated based on whether thecardiac pacing system is in a sensing mode or a pacing mode. When thecardiac system is in a pacing mode it is, itself, generating electricalsignals. This condition can alter or saturate one or more of thesensors. For example, the cardiac pacing system can be configured toalter the sense/pace filters of one or more specific sensing signalsbased on whether the cardiac pacing system is sensing or pacing. Thiscan occur based on a time duration of a single case of pacing, or basedon some percentage of time in which the cardiac pacing system is pacing.

FIG. 18 is an illustration 1800 of an exemplary process flow foraltering software filters and the active baseline algorithm in responseto providing pacing therapy. At 1802, a signal can be sensed by thecardiac pacing system. At 1804, a determination can be made as towhether the cardiac pacing system is currently pacing the patient. At1806, in response to a determination that the cardiac pacing system iscurrently providing pacing therapy, the software filters can be alteredto maintain an appropriate baseline from the resultant processed signal.At 1808, in response to a determination that the cardiac pacing systemis not currently providing pacing therapy, the noise can be filteredfrom the signal.

A cardiac pacing system can include gain amplifiers 1714. Gainamplifiers 1714 can be executed by one or more processors of the cardiacpacing system, such as may be embodied in controller 302 of pulsegenerator 102 illustrated in FIG. 3. Gain amplifiers 1714 can beexecuted by one or more processors of a programmer, such as programmer320 illustrated in FIG. 3.

Gain amplifiers 1714 can adjust the gain of the sensed signal togenerate a stable signal that is acceptable for use by downstreamalgorithms. For example, typical signal processing includes a phasewhere the analog signal is converted into the digital domain (ADC). Attimes, a gain multiplier/divider is applied to the analog and/or digitalsignal in order to improve the signal's representation to the downstreamdetection system.

Fixed and automatic gain control schemes can be used by the cardiacpacing system. Fixed gain control schemes use a specific gain for aspecified period of time. Automatic gain control schemes continuallyadjust the gain based upon the size of the sensed signal. A combinationof a fixed and automatic gain scheme can also be utilized. The cardiacpacing system selects or automatically adjusts gain schemes based upon apreferred sensing signal. For example, one gain scheme may be selectedfor ECG signals, while a differing gain scheme is selected for bloodoximetry signals.

Following filtering and other signal preparation, the cardiac pacingsystem then evaluates whether the resultant signals are of sufficientquality to be processed for downstream sensing algorithms. The cardiacpacing system continually analyzes all of the available sensed signalsagainst their corresponding set of acceptability requirements.Acceptability factors include signal amplitudes, signal-to-noise ratios,signal widths, frequency spectrum and time ratios. The acceptabilityfactor for any particular signal can be further modified based uponother factors such as heart rate, posture, time of day or uponinformation provided by other sensors from the cardiac pacing system.For any particular sensed signal, there is a minimum acceptability scorethe signal must pass. A signal is discarded from further evaluation ifthe signal is below the minimum acceptability score. If the signalquality is passing, the signal continues to be processed, evaluated andanalyzed.

While the cardiac pacing system analyzes numerous physiologicalcharacteristics such as the patient's electrocardiogram, respiration,blood oximetry, temperature, and the like, the signal selectionalgorithm gives preference to those signals that result in the highestsensitivity and specificity for triggering detections in response to aheartbeat or other events of interest such as skeletal musclecontraction. As such, the signal selection algorithm can dynamicallypreference certain sensed signals over others. Therefore, while severalphysiological signals are deemed equally usable because they receivepassing acceptability scores, the signal selection algorithm can applygreater weight to certain signals (e.g., electrocardiogram) to otherpassing signals (e.g., respiratory rate) because they are moredeterministic for triggering heartbeat detections. The signal selectionalgorithm can use a predetermined signal preference order, oralternatively, the signal preference order can be weighted differentlybased upon certain factors such as signal amplitude, signal-to-noiseratio, signal width, timing ratios and the like.

In certain circumstances, the cardiac pacing system assesses multiplesignals for the same physiological characteristic. For example,respiratory rate signals from two different sensing pairs receivepassing acceptability scores. The signal selection algorithm can analyzeand select the sensing signal resulting in the best signal forelectrocardiogram analysis. Alternatively, the signal selectionalgorithm can combine two or more signals in a manner that yields animproved composite signal for sensing evaluation. Different mathematicalprocesses can be applied to each or combined signal(s) to yield thedesired composite sensing signal. These processes may includesumming/subtracting signals, multiplying or dividing one signal fromothers, combining the differentiated or integrated signal from othersignals or other mathematical combinational methods

A cardiac pacing system can include a smart switch algorithm. The smartswitch algorithm can automatically initiate additional sensing andprepare to switch to an alternative sensing signal in response tocertain defined detected events. The smart switch algorithm can beconfigured to monitor certain detected events. Examples of detectedevents the smart switch algorithm can monitor include signal amplitude,heart rate, posture, pace/sense modes, and/or other characteristics ofthe heart, patient, and/or cardiac pacing system. Upon sensing such adetected event, the smart switch algorithm can automatically switch theprimary sensing signal to an alternative sensing signal uponconfirmation of such detected event. For example, the manner in whichsignals travel through the body can change if the patient's posturechanges from supine to standing. Consequently, a particular sensingsignal may be the most appropriate signal in one posture, butineffective in a second posture. As a result of programming, or learningfrom previous events, the smart switch algorithm can anticipate theinappropriateness of the signal selection based on the detected eventand prophylactically switches to alternative sensing signal(s).

As an example, a first sensor can be disposed in the patient's body andconfigured to detect a first physiological characteristic of thepatient. A pulse generator, receiving signals from the first sensor canbe configured to have the first physiological characteristic being theprimary physiological characteristic for monitoring by the cardiacpacing system. An event can occur that saturates the sensingcapabilities of the first sensor, making the sensor ineffective atdetecting whether or not the heart is functioning properly. The smartswitch algorithm can be configured to select a second physiologicalcharacteristic as being the primary physiological characteristic formonitoring by the cardiac pacing system in response to the first sensorbecoming saturated. For example, if the amplitude of the ECG increasesdue to changes in posture, resulting in ECG amplifier saturation, thesmart switch algorithm can switch to monitoring pressure waves generatedby the heart.

The cardiac pacing system can use the resultant processed sensingsignal(s) to analyze whether pacing a patient's heart is appropriate.Accurately sensing atrial and ventricular activity enables the cardiacpacing system to assess the need for therapy delivery, and theappropriate pacing mode for the patient.

The cardiac pacing system of the present disclosure can be configured tomonitor the activity and origin of a sensed cardiac signal. The cardiacpacing system can be configured to detect the functioning of the cardiacmuscles and to provide therapy accordingly. In some variations, thecardiac pacing system can detect the functioning of the cardiac musclesusing one or more accelerometers.

Sensitive accelerometers can be configured to detect motion of cardiactissue. Accelerometer(s) can be disposed adjacent the heart of thepatient. For example, accelerometer(s) can be placed in the mediastinum,intercostally, and/or in other locations suitable for sensing. Theaccelerometer can be configured to measure the degree of motion impartedonto the accelerometer by the beating heart.

A beating heart causes a pressure wave to be emitted from it. Theaccelerometer can be configured to detect the localized tissue movementdue to the pressure wave and provide indications on the functionality ofthe heart by analyzing the resultant signal. However, the accelerometercan also be affected by exogenous motion attributable to other factors,such as movement of the patient, breathing, sound waves, and the like.In certain instances, this exogenous motion can dwarf the motionattributable to the pressure waves from the heart.

Exogenous motion can be filtered from the received signals using acombination of hardware and software filters as previously described.Exogenous motion can be also be filtered from the received signals whenat least two sources are used to facilitate the detection of the motionof the heart. Subcutaneous accelerometer(s) (SA) can be placed, forexample, on the pectoral region of the patient. A second heartaccelerometer (HA) can be placed adjacent the heart, for example, on alead inserted through the intercostal space in the region of theanterior mediastinum. Movement of the heart causes pressure wavestravelling through tissues of the patient to be detected by bothaccelerometers, but each accelerometer receives a different signal basedon the path taken and the interference or exogenous motion added duringpropagation of the signal. In some cases, the intensity of theinterference or exogenous motion can far exceed the intensity of anypressure wave attributable to the functioning of the heart.Consequently, the interference or exogenous motion detected by theaccelerometers can dwarf the pressure wave signal attributable to theheart.

The SA can be configured to transmit subcutaneous vibrationmeasurement(s) to the pulse generator. The HA can be configured totransmit a cardiac vibration measurement to the pulse generator. Thepulse generator can be configured to factor the subcutaneous vibrationmeasurement(s) from the SA into the cardiac vibration measurement fromthe HA to assess a physiological characteristic of the heart. In somevariations, the factored vibration measurement can be processed usingone or more filters. In some variations, the cardiac vibrationmeasurement and/or the subcutaneous vibration measurement can beprocessed using one or more filters prior to being factored. Theresultant vibration measurement can provide a desired signal that thecardiac pacing system can analyze to assess heart functionality.

In some variations, the SA can be disposed within the housing of thepulse generator, at the end of a lead disposed within the patient, andthe like. In some variations, multiple HA and SA accelerometers can beused. The multiple HAs and SAs can be disposed at different locationsthroughout the body. For example, multiple HAs can be disposed about theheart. The HAs being at different locations can facilitate determinationof the movement, or beating, of different portions of the heart. In thismanner, a virtual model of the complete functionality of the heart canbe generated which can form the basis of adjustments to the pacing bythe cardiac pacing system.

Triggering of certain heartbeat detections can be performed by thecardiac pacing system using one or more acoustic sensors. Acousticsensors function similarly to a stethoscope. As such, acoustic sensorscan be configured to detect sound waves generated by the heart. Thecardiac pacing system can sense and analyze sound wave signals todetermine whether or not pacing therapy is required. Analysis of thesensed sound wave signals can include identification of known sounds,such as the sounds made when the mitral and tricuspid valves close (S1sounds). Analyzing sound waves can be an effective way to separateT-wave signals, a period of relatively little acoustic pressure, fromQRS complex and S1 sounds, when T-wave signals become a prominentcomponent of the ECG signal. The cardiac pacing system can be configuredto use filters, such as the filters described herein, to separateexogenous sounds from the cardiac sounds prior to the analysis byalgorithms of the cardiac pacing system.

FIG. 19A is an example of an ECG 1901 of a patient having prominentT-wave signals. FIG. 19B is an example of a simultaneous acoustic signal1902. These figures demonstrate that acoustic signals can be used todistinguish desirable signal attributes such as ventriculardepolarization (the R-wave on the ECG and the S1 from the heart soundsignal) from undesirable signal attributes such as ventricularrepolarization (the T-wave on the ECG and the S2 from the heart soundsignal). In this example, the corresponding T-wave event on the acousticsignal is less prominent than the same T-wave event shown on the ECG.

FIG. 20 is an illustration 2000 of an exemplary process flow forprocessing acoustic signals obtained by the cardiac pacing system,having features consistent with the present disclosure. At 2002, anacoustic signal can be obtained by the cardiac pacing system. At 2004,the signal can be dynamically filtered using the dynamic filteringalgorithm and techniques described in the present disclosure. At 2006, adetermination can be made as to whether the signal exceeds a detectionthreshold. At 2008, in response to a determination that the signal doesnot exceed a detection threshold, the cardiac pacing system can beconfigured to deliver a pacing pulse. At 2010, in response to adetermination that the signal does exceed a detection threshold, it canbe determined that a pacing pulse is not required. At 2012, in responseto no pacing pulse being required at 2010, or in response to thedelivery of a pulse at 2008, the cardiac pacing system can be configuredto restart the analysis to determine the need for the next pace pulse.

In some variations, the acoustic signal, generated by the sound wavescaused by the beating heart, can be captured via an accelerometerlocated on an implanted lead. In some variations, an accelerometer canbe used where an acoustic sensor cannot.

The cardiac pacing system can be configured to monitor the functionalityof particular chambers of the heart such as the atria. The functioningof the particular chambers of the heart can be monitored in similarmanners as the general cardiac sensing techniques described herein.Additionally, the filtering techniques described in the presentdisclosure apply equally to atrial sensing as they to do to ventricularsensing, and sensing of the heart generally.

The cardiac pacing system can include multiple sensors at multiplesensing vectors around the heart. The sensing vectors can be atpredefined locations, or along predefined planes, relative to thepatient's heart. The sensors creating the multiple sensing vectors canbe configured to triangulate, and therefore pinpoint, the location of asource of a signal and determine how and where the signal ispropagating.

ECG signals can propagate from the heart through other anatomicalstructures within the body. The propagation of the ECG signal can beobtained by the multiple sensors. The cardiac pacing system can beconfigured to process the propagated signals to determine if the sourceof the ECG signal originates from higher within the thorax, near theatrium of the heart, or lower within the thorax, near the ventricle ofthe heart.

For example, a sensor on the pulse generator (SPG) placed over thesternum will have a unique angle and shorter distance to the atria thanan alternative sensor (SA) placed in the intracostal space inferior tothe pulse generator. Signal analyses of a particular feature can beperformed to determine differences in amplitudes and relative timing.Due to proximity, the feature as measured from SPG will have largeramplitude and occur before the feature as it is measured from SA. Thesetiming relationships can be used to determine whether the origin of thesignal is atrial or ventricular in nature and the direction of signalpropagation.

In some cases, alignment of various elements of the cardiac cycle may beused for timing comparison between sense vectors. These features caninclude the onset (starting point), completion (ending point),mid-point, inflection point, zero-slope point, positive peak (signalmaximum), negative peak (signal minimum), steepest slope, or area underthe curve of a particular portion of the ECG (P-wave, QRS, T-wave,etc.). These alignment points can be compared across multiple sensevectors to identify timing relationships. Additionally, multiplealignment points can be combined during the comparative analysis with analternate sense vector. Signal elements from other non-ECG sensors(accelerometer, blood oximetry, pulse pressure, etc.) can also be usedfor alignment purposes.

The cardiac pacing system can be designed with a dedicated signaltriangulation circuit or real-time algorithm that continually outputsthe calculated source location of the signal source. The output of thesignal triangulation can consist of a matrix ID or a grid coordinatemethod to represent the location of the signal source. This output canbe calibrated for the patient automatically by the cardiac pacing systemor with physician input via a programmer, such as programmer 320 in FIG.3. For example, following implantation of the cardiac pacing system, acalibration routine can be used to analyze the real-time signals frommultiple ECG vectors available from the cardiac pacing system. Thiscalibration can include input from the physician to specify or confirmthe P-wave or R-wave elements of the ECG. Once confirmed, the cardiacpacing system can identify the range of coordinates that each real-timesignal represents, and the direction of the signal's propagation.

Signal triangulation can guide therapy delivery for the cardiac pacingsystem. For example, signal triangulation can be used to identifyinstances when an atrial signal does not conduct to the ventricle. Inthese instances, the cardiac pacing system can deliver a ventricularpacing pulse to assist with proper cardiac conduction. Alternatively,signal triangulation can be used to confirm intrinsic ventriculardepolarization and inhibit pacing therapy.

FIG. 21A is an illustration 2100 of an exemplary process flow for anatrial template reference having features consistent with the currentsubject matter. An atrial template reference can use a known templatefor a particular signal for comparison against a signal detected by oneor more sensors of the cardiac pacing system. This comparison can beperformed to find P-waves on a live streaming signal. The atrialtemplate signal can be collected by a programmer, such as programmer 320of FIG. 3, and fed into a controller, such as controller 302 of FIG. 3.In some variations, the template can be stored within electronic storageof the pulse generator, such as electronic storage 308 of FIG. 3. Insome variations, multiple templates can be obtained that reflect thesignal template when the patient is in different postures, has differentheart rates, for different sense vectors, and other like parameters.

During sinus rhythms, the interval between consecutive P waves does notchange significantly on a beat-to-beat basis. Consequently, the cardiacpacing system can be configured to use an “expectation window” todetermine when in time a subsequent P-wave would be expected to occur.FIG. 21B is an illustration of a P-wave signal illustrating an“expectation window.” Within this window, the signal can be analyzed andcompared to the known template in order to confirm the presence of aP-wave. By limiting this analysis to the expectation window, falsepositive matches to other signal features such as the T-wave can beavoided or minimized.

Expectation windows can also be used to identify irregular P-waveintervals indicative of atrial arrhythmias. In response to identifyingthese irregular intervals, the pacing mode or other settings can beautomatically altered to ensure appropriate pacing therapy continues.Settings can then automatically revert back to the previous settingswhen regular intervals are identified and the arrhythmia terminates.

AV delays can be similarly triggered once a P-wave is confirmed. The AVdelay can also be adjusted based on the timing location of the peak,onset, termination, and the like, of the P-wave. In some variations, the“expectation window” can be based on a combination of average heart ratefor the patient and the preceding P-P interval or R-R interval. Theduration of the expectation window can also be automatically shortenedor lengthened based upon the heart rate, or adjusted via the programmer.

At 2102, the average heart rate (HR) of the patient can be obtained. At2104 the instant HR of the patient can be obtained. At 2106, the averageHR and the instant HR can be used to determine the P-wave expectationwindow. At 2108, the atrial template reference can be used to find theP-wave. At 2110, the AV delay can be initiated and adjusted for thedetected P-wave peak timing.

While expectation windows have been disclosed with reference to atrialsignals, the description is additionally applicable for ventricularsignals. For example, expectation windows can be used to determine whenin time a subsequent R-wave would be expected to occur.

Following the filtering stage and selection of the preferred sensingsignals for analysis, the cardiac pacing system can then analyze thesesignals for heartbeat detections and assess the need for therapydelivery. FIG. 22 is an illustration of an exemplary process flow 2200for analyzing sensed signals for the triggering and authentication ofheartbeat detections, having features consistent with the presentdisclosure.

Detection profiles are used to trigger heartbeat detections from aselected sensing signal. A detection profile is a threshold value usedfor comparison with the preferred sensing signal. If the sensing signalexceeds the detection profile threshold, a heartbeat detection istriggered. If the sensing signal remains below the detection profilethreshold, sensing continues until a heartbeat detections is triggered.

Detection profiles can take many forms and are based upon the type ofsensing signal being analyzed. A horizontal, equipotential level(horizontal line) is an example of a detection profile. In this example,a fixed horizontal detection profile of 5 mV will trigger a heartbeatdetection when the sensing signal exceeds the 5 mV detection profilethreshold. The detection profiles can include horizontal (equipotential)elements, decaying elements of various shapes such as fixed slope,exponential decays, and the like, increasing slope elements of variousshapes such as fixed slope, exponential growths, and the like, or acombination of elements.

Detection profiles are selected based upon the type of sensing signalbeing analyzed. Similarly, multiple detection profiles can be used for aparticular sensing signal. For example, the cardiac pacing system willselect a detection profile designed for ECG sensing over a detectionprofile for a respiration signal when analyzing an ECG signal.Similarly, the cardiac pacing system will select a detection profiledesigned for atrial ECG sensing over a detection profile for ventricularECG sensing when analyzing an ECG signal for P-waves by the sensingalgorithms described herein.

Detection profiles can include periods where heartbeat detections aretemporarily inhibited. Such periods can be used immediately followingthe triggering of an initial heartbeat detection in order to prevent asubsequent erroneous heartbeat detection for some period of time.Furthermore, heartbeat detections from one sensing signal may initiatenon-detection periods on alternate sensing signals.

Elements of the detection profile and non-detection windows can beautomatically adjusted based upon attributes of the sensing signal suchas mode of pacing, ectopic cardiac events, signal amplitude, heart rate,time of day or other sensor input such as accelerometer or posture, andthe like.

Morphology comparison methods can be used as a means to triggerheartbeat detections and identify the occurrence of specific cardiacevents. This comparison method may be performed in real-time usingmorphology detection algorithms or hardware circuitry. For example, ifthe morphological shape of a ventricular depolarization is known from anECG signal, a template of that known shape can be created and used forsubsequent comparison. The template can then be continually scanned inreal-time throughout the sensing signal to identify when the known shapereoccurs. When a pattern match is noted, a heartbeat detection can bedeclared. As a result, this method can identify the occurrence of asubsequent ventricular depolarization.

The template can be collected by a programmer, such as programmer 320 ofFIG. 3, and fed into a controller, such as controller 302 of FIG. 3. Insome variations, the template can be automatically generated and storedwithin electronic storage of the pulse generator, such as electronicstorage 308 of FIG. 3. Historical templates can be used to generate orupdate a primary template, or a primary template can be a based upon thecompilation of some number of previous heartbeat detections.

In some variations, multiple templates can be obtained that reflect thetemplate when the patient is in different postures, has different heartrates, for different sense vectors, and for other like parameters.Furthermore, the selection of the appropriate template for comparisoncan be automatically updated based upon factors including pacing mode,heart rate, posture, time of day or other measures of the input signals.Alternatively, several measured or artificially created templates can bestored by the cardiac pacing system and used for the morphologydetection algorithms.

Different elements of sensed signals can be used for comparisonpurposes. For example, ventricular depolarizations may be used to storethe ventricular signal template, while a separate signal template isstored for atrial depolarization detections. Furthermore, non-heartbeatsignals and templates can be used for morphology comparisons. Forexample, a unique shape of the respiration signal can be used to countthe number of breaths per period of time, indicative of the respiratoryrate.

Morphology comparison methods can be performed with software and/orhardware processing. Automatic adjustment of the signal or storedtemplate can be performed prior to or during the morphology comparisonprocess. Such adjustments include scaling methods of the amplitude orwidth, time shifting of either the signal or stored shape, or the like.

Morphology detection methods can be used independently, or inconjunction with certain detection profiles. For example, a detectionprofile can be used first to trigger a heartbeat detection. This initialheartbeat detection can then initiate a morphology comparison algorithmto confirm or call into question the initial heartbeat detection.Alternatively, both algorithms may be operating in parallel toindependently evaluate heartbeat detections.

Alternative sensing methods can be analyzed to confirm or questioncertain sensing signals collected by the cardiac pacing system. Sensorscollecting information regarding a patient's activity and respirationrate provide the cardiac pacing system additional analysis tools toconfirm heartbeat detections and assess the need for therapy delivery.

Activity sensors can be used to determine the current activity levels ofthe patient. Activity sensors such as accelerometers can be used toindicate patient movement and activity and can be, for example,incorporated into an implanted pulse generator housing. Theaccelerometer signal can be analyzed to determine the degree of movementby the patient. As patient movement increases, heart rate demandsgenerally rise as well.

An algorithmic comparison of the actual versus ideal heart rate for anygiven degree of movement can be used to automatically adjust a cardiacpacing system's rate-responsive pacing rate. If the activity sensorindicates a high degree of patient movement, yet the measured heart ratefalls below the ideal heart rate by a pre-determined range, the pacingrate may be temporarily increased. The degree of heart rate increase isrelated to the degree of activity, up to a predetermined maximum pacingrate. Conversely, when the activity sensor indicates less motion, thepacing rate can be reduced over-time to some pre-determined lower pacingrate.

Filtering of the accelerometer signal can separate outside motion fromthe actual movement of the patient. For example, filtering can be usedto separate the motion from a patient sitting calmly in their car ascompared to a patient running up a set of stairs.

Respiration sensing can be used to determine the current activity levelsof the patient. As a patient's activity increases, oxygen demandgenerally increases and the respiration rate and volume increaseaccordingly. By detecting these changes in respiration, heart raterequirements can be assessed. If respiration rate and/or volume increasewithout a correlative heart rate increase, the pacing rate can beautomatically increased to improve hemodynamic response for the patient.

Respiration sensing can be used in conjunction with activity sensing toimprove the cardiac pacing system's response. If an activity increase isnoted and a correlative respiration increase is not observed, exogenousnoise activity can be suspected. The cardiac pacing system can analyzeadditional sensed signals to assess whether the discrepancy is noiserelated. If so, the cardiac pacing system can alter its primary sensingprofile to an alternative sensing profile in efforts to avoid thediscrepancy and assess an actual heart rate. Additionally, theinformation about the discrepancy can be retained by the cardiac pacingsystem as a detected event for future smart switch algorithm usage.

Leads and electrodes placed in locations consistent with the currentsubject matter will be in relatively close proximity to the lungs. Thisproximity to the lung can facilitate several methods to assess changesin lung status such as pulmonary edema. Methods to detect changes inlung fluid status include the delivery of sub-stimulation levels ofenergy with a pacing vector that includes a portion of the lung tissue.Changing fluid levels in the lung will result in changes in measuredimpedance.

Changes in pulmonary status are generally caused by heart failure orother cardiac conditions requiring medical treatment. As such, sensedchanges in lung status can be communicated to the physician at in-personvisits or remotely to facilitate appropriate medical treatment.Additionally, the pacing mode, pacing rate and pacing energy can beautomatically adjusted in response to changes in lung status.

Leads and electrodes placed in locations consistent with the currentsubject matter can include temperature probes. Temperature measurementswithin the mediastinum can be recorded by the cardiac pacing system andprovided to a physician during in-person visits or remotely. Recordingtemperature data over time creates a normal temperature pattern.Aberrations in the normal temperature pattern can be detected andcommunicated to a physician so a definitive diagnosis and appropriatemedical treatment can be performed and prescribed. Additionally, thepacing mode, pacing rate and pacing energy can be automatically adjustedin response to temperature changes.

Authentication is a confirmation process used to ensure the accuracy ofthe sensing signal(s) and that the subsequent heartbeat detections orinhibition decisions made by the cardiac pacing system are appropriate.The authentication process utilizes algorithms to analyze heartbeatdetection decisions from multiple signal inputs and multiple signalprocessing steps for a consistent decision. If discrepancies are foundfrom one input or process to another, the cardiac pacing system canchange the sensing signal or detection process that consistently makesthe most appropriate heartbeat detection decisions.

The authentication process continually monitors all of the acceptablesignals to ensure they all yield similar heartbeat detections. Topreserve energy for the cardiac pacing system, the authenticationprocess can be initiated randomly to test the system's performance.Should repeated errors in performance be noted, the frequency andintervals of the authentication process can be adjusted until reliableheartbeat detections are observed. Alternatively, every time a heartbeatdetection is triggered on the primary sensing channel, the sensingsignals or detection processes of the alternate channels can bemonitored to ensure that they would have also triggered a heartbeatdetection; however, these additional signals can be post-processed inbatches of 5-sec segments, or within another time window and frequencythat is considerate of power consumption by the system.

In instances when sensing algorithms trigger a heartbeat detection andsubsequently inhibit a pace pulse, algorithms used in the authenticationprocess will confirm that the heartbeat detection was accurate and notan over-detection of some non-cardiac event. Conversely, if a pacingpulse is required, algorithms used in the authentication process willconfirm that an intrinsic beat was not missed. If some quantity ofnon-agreements are noted, algorithms such as the signal selectoralgorithm can be initiated to ensure that the current primary sensingvector is still the most robust of those options available for thesystem.

The cardiac pacing system can be configured to verify whether deliveryof therapeutic pulses is required. This verification can be performedusing one or more sensors. For example, the cardiac pacing system canuse a multiple trigger authentication. Multiple trigger authenticationuses multiple input signals to confirm whether a pacing pulse isrequired. As an example, the cardiac pacing system can have its primarysensing signal set to the ECG input from the sensors configured tomonitor the ECG of the patient's heart. The ECG will not trigger aheartbeat detection if the ventricle does not beat; however, a QRSsignal amplitude decrease can lead to a “missed” heartbeat detection. Asecond input signal can be used to confirm what the QRS signalindicates. For example, simultaneous monitoring of the heart sound, suchas with acoustic sensors or accelerometers, can be used to confirmwhether or not the ventricle beat. Heart sounds lag the ECG electricalresponse signal, making the use of heart sounds as the secondaryconfirmation signal especially useful.

FIG. 23 is an illustration 2300 of an ECG reading over time togetherwith a time synchronized heart sound signal reading over time. As shownin FIG. 23, the S₁ heart sound, representing the ventricular pressurewave, 2302 lags the QRS complex from the ECG reading 2304 associatedwith the ventricular depolarization. Other heart sounds S₂, S₃ and S₄may also be used to identify specific normal or abnormal cardiacactivity for the purposes of adjusting, inhibiting or delivering therapyor providing diagnostic feedback regarding the patient to the physician.

FIG. 24 is an illustration of an exemplary process flow 2400 forverifying a lack of heart beat having features consistent with thecurrent subject matter. Process flow 2400 is provided as an example of aprocess that could be performed by the cardiac pacing system to verifywhether or not the ventricle, for example, has stopped beating. At 2402,the ECG signal can be obtained by the cardiac pacing system. At 2404,the ECG signal can be filtered. The filtering can include filteringtechniques consistent with the present disclosure. At 2406, the ECGsignal can be monitored for a duration of time consistent with a desiredpacing rate. In response, at 2408, a determination can be made as towhether the signal exceeds a detection threshold using heartbeatdetection techniques consistent with the present disclosure. If thesignal does not exceed a detection threshold, then reference to theacoustic signal detection can be made.

At 2410, an acoustic signal can be obtained by the cardiac pacingsystem. At 2412, the acoustic signal can be dynamically filtered by thecardiac pacing system. At 2414, a determination can be made as towhether the acoustic signal exceeds the detection threshold. If theacoustic signal does exceed the detection threshold, then, at 2416, nopacing is required and monitoring of the heart can proceed. If, at 2414,the acoustic signal does not exceed the detection threshold, then, at2418, a determination of whether a therapeutic pulse is required fordelivery to the heart can be made. At 2420, in response to determining apulse is required, the ECG sensors can be modified in order to improvethe accuracy for triggering heartbeat detections. For example, therange, gain, and/or other parameters of the ECG can be modified. At2422, a therapeutic pulse can be delivered to the heart. Subsequently,the signals can be monitored.

Sensing for heartbeat detections must operate in real-time as pacing istriggered on a beat-to-beat basis. Lagged real-time analysis is anauthentication process that runs in a delayed fashion allowing for theprocessing of additional data that was not otherwise available at thevery moment the real-time decision was made. Following an initialheartbeat detection, the lagged real-time analysis will continue togather data and, following the post-processing of that data, canultimately over-rule the primary detection decision, resulting in adecision to deliver a therapeutic pace pulse. For example, if theprimary triggering mechanism for heartbeat detections uses the ECGsignal with an exponentially decaying detection profile, and a sensedevent is triggered, it will subsequently specify that the pacing pulseshould be inhibited. The lagged real-time analysis can continue togather data and, using a previously stored morphology template, cancompare data that occurred after the primary detection to the morphologytemplate. This analysis can confirm that the primary detection was infact triggered by the desired event and not an over-sensing of someother ECG segment or non-cardiac signal. The additional data collectioncan be of a varying period of time such as 10% of the previous R-Rinterval, or other periods of fixed or relative time.

Alternatively, if the primary triggering mechanism for heartbeatdetections indicates that no-sensed event occurred, pacing will beinitiated. The lagged real-time analysis may optionally include afirst-pace delay feature that intentionally delays or overrules a pacingpulse delivery decision if a pacing pulse has not been delivered forsome preset period of time. For example, no pacing pulses have beendelivered for 10 minutes; however, the real-time primary detectionsuddenly indicates that a pace pulse is required. Rather thanimmediately delivering the pace pulse, the lagged real-time analysisinvokes a 100 ms first-pace delay in order to analyze additional data toconfirm that intrinsic activity was not missed. If pacing is required,the first-pace delay is reduced or eliminated for the next paced beat.If pacing inhibition is confirmed, additional pace delays or pacing rateadjustments can be made to promote continued intrinsic heartbeats.

Lagged real-time analysis can include maximum interval thresholds toensure pacing is not inhibited for a clinically undesirable duration.

Pacing vector selection is designed to evaluate all pacing vectorchoices available in order to select the optimal pacing vector. Multiplepacing choices may be acceptable, allowing the device to have optionsfor changing the vector automatically if other sensor input suggeststhat a change is required.

Pacing vector selection compares pacing requirements for some or all ofthe pacing vector electrodes available to the cardiac pacing system. Inaddition to electrode pairs, more than two electrodes may also be usedfor pacing delivery, with one or more electrodes acting as the cathodeand one or more electrodes acting as the anode during pacing delivery.

An optimal pacing vector is one that minimizes pacing energy whilemaintaining adequate pacing energy safety margin. Analysis may includethe assessment of skeletal muscle stimulation during pacing and/or theassessment of pacing requirement changes with various patient postures,respiration sizes (deep breath), heart rates, and the like. Theresulting optimal pacing vector can be determined by combining some orall of these variables using a weighted or non-weighted scoring method.As such, the pacing vector with the lowest energy requirement may notnecessarily become the optimal pacing vector. Other vectors with lowenergy requirements that minimize other factors such as skeletal musclestimulation may be preferred.

The pacing vector selection algorithm can generate a list of allacceptable or unacceptable pacing vectors. These lists can then be usedby other algorithms to optimize particular sensor/electrode pairs forsensing and therapy delivery. For example, it is desirable to sense fromelectrodes that are not involved in delivery of therapeutic pacingpulses due to latent polarization effects. Polarization effects candegrade sensing performance of the cardiac pacing system. Allowing thesystem to utilize distinct electrodes to perform sensing and pacingfunctions enables the system to optimally select sensing pairssufficiently far away from the interface between pacing electrodes andsurrounding tissue, which is most susceptible to polarization effectseach time a pacing pulse is delivered. As such, the pacing vectorselection algorithm can work in concert with sensing algorithms toautomatically switch sensing and therapy delivery electrode pairs tooptimize system performance.

The programmer can be used during the pacing vector selection assessmentin order to provide confirmatory responses for certain pacing vectors.During in person follow-up visits, a range of amplitude and pulse widthsfor each available pacing vector configuration can be evaluated. Foreach setting, the degree of skeletal muscle stimulation and anyresulting perception of discomfort can be assessed, along with cardiacpacing thresholds. The degree of skeletal muscle stimulation can bemeasured automatically by the cardiac pacing system and/or programmer byanalyzing signals from an accelerometer, or like sensor, designed todetect skeletal muscle stimulation. The perception of any discomfort canbe provided by the patient to the physician conducting the procedure foreach pacing vector. The patient can accept or reject one or more pacingvectors during the assessment. Cardiac pacing thresholds can be measuredby the physician performing the follow-up visit or automatically by thecardiac pacing system. Factors used in the prioritization of pacingvectors include (1) cardiac capture thresholds, (2) degree of skeletalmuscle stimulation at tested outputs, (3) patient perception ofdiscomfort at tested outputs and (4) degree of separation betweencardiac capture thresholds and onset of skeletal muscle stimulation orperceived discomfort for each pacing vector. These factors may beanalyzed in one or multiple postures and across varying degrees ofactivity and heartrates. Information from the assessment can then besaved in the cardiac pacing system allowing the pacing vector selectionalgorithm to create a prioritized list of pacing vectors for futurereference. In the event that cardiac capture does not occur consistentlywith the most preferential vector, the cardiac pacing system will switchto those pacing vectors chosen as desirable by the patient.

The cardiac pacing system can incorporate energy control algorithms toassist in reducing pacing energy output, resulting in a longevityincrease for the cardiac pacing system. Energy control algorithms can beused to ensure that sufficient pacing energy is delivered to safelycapture the heart, while minimizing energy loss due to excessive safetymargins. FIG. 25 is an illustration of an exemplary process flow 2500for analyzing sensed signals to determine whether delivered energylevels and/or pacing vectors can be adjusted, having features consistentwith the present disclosure.

Pacing therapy demands are known to lessen while a patient is sleeping.Additionally, certain patient postures, such as the prone position, canreduce the pacing energy requirement for successful cardiac capture. Asa result, patients that typically, or periodically, sleep on theirchest, can require less pacing energy while sleeping as compared to therest of the day when they are upright. The sleep response algorithm canuse time of day, patient position information from an accelerometer orposture sensor, heart rate, ECG data, respiratory information or othersensed information to determine when a patient is sleeping and in whatposture. By analyzing these sensory inputs, the sleep response algorithmcan automatically reduce pacing energies or pacing rates during a sleepcycle when it is safe to do so. The sleep response algorithm may alsoadjust pace pulse delivery to be timed with the point of maximalexhalation in order to minimize the potential tissue space between theelectrode and the heart, resulting in lower pacing energy requirements.

The pacing energy reduction can be a fixed reduction or a proportionalreduction to the specific measured position. The duration of the pacingenergy reduction can be automatically adjusted or can be for a fixedperiod. In addition to adjusting the pacing energy, the sleep responsealgorithm can also adjust other pacing parameters, such as pacing rate,pacing mode, rate-response settings, or the like during the sleep cycle.

A delivered pacing pulse that successfully captures the heart will causethe heart to beat resulting in mechanical movement of the heart that ismeasurable. The mechanical response algorithm utilizes sensors connectedto the cardiac pacing system to assess mechanical movement of the heart,and adjust proper cardiac capture energy levels accordingly.

The mechanical response algorithm identifies mechanical heartdeflections following the delivery of a pacing pulse using one or moreaccelerometer signals, other posture sensors, acoustic signals, or thelike. The cardiac pacing system then gradually reduces the energy levelsuntil a mechanical heart deflection is no longer noted by the sensors,and loss of cardiac capture is suspected. Specific timing windows may beused to ensure that the mechanical sensory information is only analyzedfor a limited period of time immediately following pacing pulsedelivery. Upon loss of cardiac capture, the cardiac pacing system willincrease the energy level of the pacing pulse until cardiac capture isregained. The cardiac pacing system will then set that new energy level,with a specific safety margin of additional energy, as the new defaultpacing pulse energy level.

The mechanical response algorithm can operate continuously or operate ina periodic fashion, such as once per hour, day, week, or the like. Themechanical response algorithm can also be initiated by some othertrigger mechanism such as a change in posture, time of day, heart rate,or some other physiologic event noted on the ECG, accelerometer or othersignal. Throughout the energy reduction process, a backup pacing pulseat higher energy can be delivered in a delayed fashion to ensure thatappropriate cardiac function is maintained despite the loss of capturedue to a reduced energy pacing pulse.

A delivered pacing pulse that successfully captures the heart generallyevokes a larger and wider ECG deflection than the ECG deflection causedby an intrinsic heartbeat. The evoked response algorithm uses ECGanalysis for larger and wider deflections to determine if the deliveredpacing pulse captured the cardiac tissue. The algorithm can also assessevoked responses by evaluating simultaneous signals other than thepacing vector and measuring changes in specific intervals relative tothe time in which a pace pulse is delivered.

Immediately following pace pulse delivery, the cardiac pacing systemwill analyze the ECG to identify the evoked ECG response. If noted,successful capture is confirmed. The evoked response algorithm continuesto pace with lower and lower energies until loss of cardiac capture isnoted. The evoked response algorithm can utilize the preferred sensevector, any other ECG sense vector or physiologic signal, or anycombination of multiple signals to determine if cardiac capture wassuccessful. Upon loss of cardiac capture, the cardiac pacing system willincrease the energy level of the pacing pulse until cardiac capture isregained. The cardiac pacing system will then set that new energy level,with a specific safety margin of additional energy, as the new defaultpacing pulse energy level.

The evoked response algorithm can operate continuously or operate in aperiodic fashion, such as once per hour, day, week, or the like. Theevoked response algorithm can also be initiated by some other triggermechanism such as a change in posture, time of day, heart rate, or someother physiologic event noted on the ECG, accelerometer or other signal.

Pacing modifiers incorporate data from sensor inputs to ensuresuccessful cardiac capture and minimize skeletal muscle stimulation.Pacing modifier algorithms can modify pacing therapy as a result of thesensor inputs. For example, the effect of noise to a cardiac pacingsystem can include inappropriate inhibition of life-sustaining pacing.As a result, the cardiac pacing system can include pacing modifiers thattemporarily pace in an asynchronous mode if noise cannot be effectivelyremoved. Switching to an asynchronous pacing mode in the presence ofpersistent noise can provide a safety mechanism to help ensure pacing isnot dangerously inhibited due to noise.

Atrial arrhythmia algorithms can ensure that pacing therapy remainsappropriate in response to the initiation or termination of atrialarrhythmias. Certain atrial arrhythmias can result in highly variableconduction to the ventricles. This variability causes irregular heartrate intervals which can result in symptoms for patients. An atrialarrhythmia response algorithm can include an interval threshold methodto limit the degree of interval variability. In the event that theinterval threshold is reached without detection of an intrinsic R-wave,a pacing pulse can be delivered. The interval threshold can becalculated based upon a percentage of some number of previous R-waveintervals and may be updated periodically or on a beat-to-beat basis.Additionally, the interval threshold method can be selectively activatedsuch that it operates only once an atrial arrhythmia has beenidentified. In this example, upon termination of the atrial arrhythmia,the interval threshold method is deactivated.

The onset of an atrial arrhythmias can result in undesirable high rateor irregular ventricular pacing when the cardiac pacing system isoperating in a synchronous pacing mode such as DDD(R) or VDD(R). Toprevent undesirable pacing in the ventricles in response to an atrialarrhythmias, a maximum ventricular tracking rate threshold can be used.The cardiac pacing system will continue to pace the ventricles inresponse to atrial sensed events; however, the ventricular pacing ratecannot exceed the maximum ventricular tracking rate threshold.

Additionally, if a prolonged, highly variable or high rate atrialarrhythmia is detected, the cardiac pacing system can switch pacingmodes from a tracking mode to a non-tracking mode, such as VVI(R).Switching to a non-tracking mode will ensure that the ventricles do notpace at an undesirably rapid or irregular rate in response to the atrialarrhythmia. When the cardiac pacing system detects that the atrialarrhythmia has terminated, the cardiac pacing system can revert back toa tracking mode to continue delivering atrial synchronous ventricularpacing.

The atrial arrhythmia response algorithms can work in conjunction withother physiologic sensors. For example, upon the initiation of an atrialarrhythmia, the respiratory signal can be examined to monitor forshortness of breath and certain pacemaker settings, such as pacing rate,mode, output or the like, and automatically make pacemaker settingadjustments accordingly.

The respiratory pacing response algorithm ensures that adequate energyfor pacing is delivered to the patient during times of high respirationvolume. When oxygen demand increases (e.g., during exercise),respiratory rates and volumes increase. An electrode placed in theanterior mediastinum can be subjected to small movements as the chestmoves in response to deep inhalation/exhalation breaths. The deepbreaths can additionally cause small changes in the tissue separationbetween the electrode and the heart.

The resulting respiration signal can be used by the cardiac pacingsystem to analyze the patient's breathing patterns and identify momentsof increased respiratory volume. In response to these deep breaths, thepacing energy can be increased to ensure cardiac capture is maintained.Alternatively, the respiratory pacing response algorithm can delay thepacing pulse delivery until the point of maximum exhalation, therebyavoiding the need for increased energy at maximum inhalation. A pacingpulse can be selectively synchronized to breathing patterns in order toensure cardiac capture in an energy efficient manner. The degree ofenergy increase can be a fixed energy increase or can be proportional tothe size of respiration volume change.

The degree or method of the energy increase can be modified by thephysician using a programmer. The programmer can assist in analyzing thepatient's breathing patterns, including during deep inhalation. Pacingcapture thresholds can be determined at varying states of inhalation andthis data may be supplied to the cardiac pacing system, and used by therespiratory pacing response algorithm.

The postural pacing response algorithm ensures that adequate energy forpacing is delivered to the patient, despite changes in patient posture.Certain changes in patient posture can result in small movements of theorgans or tissue within the chest. These changes can alter theseparation between the heart and pacing electrodes used by the cardiacpacing system. For example, when a patient moves from a prone to supineposture, the distance between the patient's heart and the distal tip ofa lead placed within the anterior mediastinum can be observed.Subsequently, an increase in the pacing energy requirement forsuccessful cardiac capture can result. Other posture changes cansimilarly reduce the separation between the heart and pacing electrodesused by the cardiac pacing system, resulting in a reduction in pacingenergy requirements.

A multi-axis accelerometer, or other posture sensor, can be used by thecardiac pacing system to analyze the patient's position and identifythose positions that can affect pacing energy requirements. In responseto a positional change, the pacing vector or energy can be modifiedaccordingly to ensure the proper pacing energy is used and cardiaccapture is maintained. The degree of energy increase/reduction can be afixed or can be proportional to the relative position displacement.

The programmer 320 can be used to analyze the pacing requirements duringvarious patient postures. Pacing capture thresholds can then bedetermined at varying positions for the postural pacing responsealgorithm.

The skeletal muscle response algorithm assesses whether therapeuticpacing pulses delivered by the cardiac pacing system producedundesirable skeletal muscle stimulation. Exciting skeletal muscle canresult in muscle contractions. These muscle contractions can then bemeasured by sensitive accelerometers controlled by the cardiac pacingsystem. The muscle response algorithm can use signals from one or moreaccelerometers to compare changes in skeletal muscle deflection duringpacing to skeletal muscle deflection during intrinsic heartbeatactivity. Through the comparison, the cardiac pacing system candetermine if the skeletal muscle response is more significant duringpacing delivery. For example, the skeletal muscle response algorithm cancompare signals from one accelerometer placed on a lead disposed in theanterior mediastinum to a second accelerometer within the implantedpulse generator. If skeletal muscle stimulation is noted during pacing,the skeletal muscle response algorithm can automatically adjust thepacing output until skeletal muscle stimulation is no longer observed.The skeletal muscle response algorithm can alter voltage, pulse width ora combination of both, or can automatically switch to a different pacingvector that reduces or eliminates skeletal muscle stimulation. Theskeletal muscle response algorithm can additionally utilize other energycontrol algorithms described herein to ensure successful cardiac captureis maintained throughout the algorithmic assessment.

The programmer 320 can be used to analyze the degree of skeletal musclestimulation observed using various pacing vectors. This information canthen be calibrated with the patient's perception of the skeletal musclestimulation to generate a prioritized list of pacing vectors the cardiacpacing system should utilize for a patient, and for what circumstancescertain such pacing vectors should be adjusted if the original pacingvector possesses a high likelihood of resulting in undesirable skeletalmuscle stimulation.

The cardiac pacing system can be configured to monitor a concomitantdevice. A concomitant device can be a device that provides differentfunctionality than, for example, the cardiac pacing system consistentwith the current disclosure. The concomitant device can be, for example,an implantable cardioverter-defibrillator (ICD). The cardiac pacingsystem may be configured to facilitate pacing of the heart and rely onthe ICD to provide defibrillation for the heart. In response to anactivation of the concomitant device, the cardiac pacing system can beconfigured to dynamically change the filters used by the sensor(s)disposed within the body to account for the energy or signal noisegenerated by the concomitant device.

The cardiac pacing system can be further configured to communicate withthe concomitant device. In some variations, a pulse generator, forexample, can be mechanically or electronically attached to an ICD. Insome variations, the pulse generator and the concomitant device cancommunicate wirelessly.

While components have been described herein in their individualcapacities, it will be readily appreciated the functionality ofindividually described components can be attributed to one or more othercomponents or can be split into separate components. This disclosure isnot intended to be limiting to the exact variations described herein,but is intended to encompass all implementations of the presentlydescribed subject matter.

In the descriptions above and in the claims, phrases such as “at leastone of” or “one or more of” may occur followed by a conjunctive list ofelements or features. The term “and/or” may also occur in a list of twoor more elements or features. Unless otherwise implicitly or explicitlycontradicted by the context in which it used, such a phrase is intendedto mean any of the listed elements or features individually or any ofthe recited elements or features in combination with any of the otherrecited elements or features. For example, the phrases “at least one ofA and B;” “one or more of A and B;” and “A and/or B” are each intendedto mean “A alone, B alone, or A and B together.” A similarinterpretation is also intended for lists including three or more items.For example, the phrases “at least one of A, B, and C;” “one or more ofA, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, Balone, C alone, A and B together, A and C together, B and C together, orA and B and C together.” Use of the term “based on,” above and in theclaims is intended to mean, “based at least in part on,” such that anunrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems,apparatus, methods, and/or articles depending on the desiredconfiguration. The implementations set forth in the foregoingdescription do not represent all implementations consistent with thesubject matter described herein. Instead, they are merely some examplesconsistent with aspects related to the described subject matter.Although a few variations have been described in detail above, othermodifications or additions are possible. In particular, further featuresand/or variations can be provided in addition to those set forth herein.For example, the implementations described above can be directed tovarious combinations and subcombinations of the disclosed featuresand/or combinations and subcombinations of several further featuresdisclosed above. In addition, the logic flows depicted in theaccompanying figures and/or described herein do not necessarily requirethe particular order shown, or sequential order, to achieve desirableresults. Other implementations may be within the scope of the followingclaims.

What is claimed is:
 1. A cardiac pacing system comprising: a firstsensor configured to detect a first physiological characteristic of apatient; a second sensor configured to detect an alternativephysiological characteristic of the patient; and a controller configuredto: monitor the first physiological characteristic of the patient todetermine whether a heart of the patient is functioning properly;monitor the patient for a detected event; and switch from monitoring thefirst physiological characteristic to monitoring the alternativephysiological characteristic when the detected event occurs, theswitching further based on determining that a signal from the firstsensor is inappropriate for monitoring heart function.
 2. The cardiacpacing system of claim 1, wherein the first sensor is an ECG sensor andthe detected event is a change in posture that results in saturation ofthe ECG sensor that renders the ECG sensor ineffective at detectingwhether a heart of the patient is functioning properly.
 3. The cardiacpacing system of claim 1, wherein the first physiological characteristicand the alternative physiological characteristic are selected from thegroup consisting of: a heart rate, a respiration rate, a blood oximetrylevel, a temperature, a pH level, and a pressure, the alternativephysiological characteristic being different from the firstphysiological characteristic.
 4. The cardiac pacing system of claim 1,wherein the detected event is a change in a posture of the patient. 5.The cardiac pacing system of claim 1, wherein the detected event is aheart rate or other detected characteristic of the heart of the patient.6. The cardiac pacing system of claim 1, wherein the determiningincludes detection of saturation of a sensing capability of the firstsensor.
 7. The cardiac pacing system of claim 1, wherein after theswitch, the alternative physiological characteristic is monitored todetermine whether the heart is functioning properly.
 8. The cardiacpacing system of claim 1, wherein the switch is performed based on theswitch algorithm learning from previous detected events.
 9. A computerprogram product comprising a non-transitory, machine-readable mediumstoring instructions which, when executed by at least one programmableprocessor, cause operations comprising: monitoring a first physiologicalcharacteristic of a patient with a first sensor configured to detect thefirst physiological characteristic to determine whether a heart of thepatient is functioning properly; monitoring the patient for a detectedevent; determining that a signal from the first sensor is inappropriatefor monitoring heart function; and switching, when the detected eventoccurs, from monitoring the first physiological characteristic tomonitoring an alternative physiological characteristic detected with asecond sensor, wherein the switching to monitor the alternativephysiological characteristic is further based on the determining thatthe signal from the first sensor is inappropriate for monitoring heartfunction.
 10. The computer program product of claim 9, wherein the firstsensor is an ECG sensor and the detected event is a change in posturethat results in saturation of the ECG sensor that renders the ECG sensorineffective at detecting whether a heart of the patient is functioningproperly.
 11. The computer program product of claim 9, wherein the firstphysiological characteristic and the alternative physiologicalcharacteristic are selected from the group consisting of: a heart rate,a respiration rate, a blood oximetry level, a temperature, a pH level,and a pressure, the alternative physiological characteristic beingdifferent from the first physiological characteristic.
 12. The computerprogram product of claim 9, wherein the detected event is a change in aposture of the patient.
 13. The computer program product of claim 9,wherein the detected event is a heart rate or other detectedcharacteristic of the heart of the patient.
 14. The computer programproduct of claim 9, the determining including detecting of saturation ofa sensing capability of the first sensor.
 15. The computer programproduct of claim 9, the operations further comprising: monitoring thealternative physiological characteristic after the switching todetermine whether the heart is functioning properly.
 16. The computerprogram product of claim 9, wherein the switching is performed based onthe switch algorithm learning from previous detected events.
 17. Acardiac pacing system comprising: a first sensor configured to detect afirst physiological characteristic of a patient, wherein the firstsensor is an ECG sensor; a second sensor configured to detect analternative physiological characteristic of the patient; and acontroller configured to: monitor the first physiological characteristicof the patient; monitor the patient for a detected event, wherein thedetected event is a change in posture that results in saturation of theECG sensor that renders the ECG sensor ineffective at detecting whethera heart of the patient is functioning properly; and switch frommonitoring the first physiological characteristic to monitoring thealternative physiological characteristic when the detected event occurs.18. The cardiac pacing system of claim 17, wherein the firstphysiological characteristic and the alternative physiologicalcharacteristic are selected from the group consisting of: a heart rate,a respiration rate, a blood oximetry level, a temperature, a pH level,and a pressure, the alternative physiological characteristic beingdifferent from the first physiological characteristic.
 19. The cardiacpacing system of claim 17, wherein the switch is performed based on theswitch algorithm learning from previous detected events.
 20. A computerprogram product comprising a non-transitory, machine-readable mediumstoring instructions which, when executed by at least one programmableprocessor, cause operations comprising: monitoring a first physiologicalcharacteristic of a patient with a first sensor configured to detect thefirst physiological characteristic, wherein the first sensor is an ECGsensor; monitoring the patient for a detected event; and switching, whenthe detected event occurs, from monitoring the first physiologicalcharacteristic to monitoring an alternative physiological characteristicdetected with a second sensor, wherein the detected event is a change inposture that results in saturation of the ECG sensor that renders theECG sensor ineffective at detecting whether a heart of the patient isfunctioning properly.
 21. The computer program product of claim 20,wherein the first physiological characteristic and the alternativephysiological characteristic are selected from the group consisting of:a heart rate, a respiration rate, a blood oximetry level, a temperature,a pH level, and a pressure, the alternative physiological characteristicbeing different from the first physiological characteristic.
 22. Thecomputer program product of claim 20, wherein the switching is performedbased on the switch algorithm learning from previous detected events.23. A cardiac pacing system comprising: a first sensor configured todetect a first physiological characteristic of a patient; a secondsensor configured to detect an alternative physiological characteristicof the patient; and a controller configured to: monitor the firstphysiological characteristic of the patient; monitor the patient for adetected event, wherein the detected event is a change in a posture ofthe patient; and switch from monitoring the first physiologicalcharacteristic to monitoring the alternative physiologicalcharacteristic when the detected event occurs.
 24. The cardiac pacingsystem of claim 23, wherein the first physiological characteristic andthe alternative physiological characteristic are selected from the groupconsisting of: a heart rate, a respiration rate, a blood oximetry level,a temperature, a pH level, and a pressure, the alternative physiologicalcharacteristic being different from the first physiologicalcharacteristic.
 25. The cardiac pacing system of claim 23, wherein theswitch is performed based on the switch algorithm learning from previousdetected events.
 26. A computer program product comprising anon-transitory, machine-readable medium storing instructions which, whenexecuted by at least one programmable processor, cause operationscomprising: monitoring a first physiological characteristic of a patientwith a first sensor configured to detect the first physiologicalcharacteristic; monitoring the patient for a detected event, wherein thedetected event is a change in a posture of the patient; and switching,when the detected event occurs, from monitoring the first physiologicalcharacteristic to monitoring an alternative physiological characteristicdetected with a second sensor.
 27. The computer program product of claim26, wherein the first physiological characteristic and the alternativephysiological characteristic are selected from the group consisting of:a heart rate, a respiration rate, a blood oximetry level, a temperature,a pH level, and a pressure, the alternative physiological characteristicbeing different from the first physiological characteristic.
 28. Thecomputer program product of claim 26, wherein the switching is performedbased on the switch algorithm learning from previous detected events.